I think there will always be interest in any timeline that has a Prince Arthur surviving.
Few points that might help.
1) The Anglo-Spanish alliance in OTL was weak and got weaker - largely due to the fact that Catherine's father was quite happy to ignore his English ally (OTL Henry VIII) for his own gain - in fact the first breach came pretty early in Henry VIII's reign much to Catherine's distress. There is no guarantee with Arthur's succession that will change.
2) Throughout the 1510's, 20s and 30s - England would switch positions and alliances as would most of her neighbours - political marriages across Europe rarely resulted in a close long-lasting political alliance between the nations involved.
3) There was a strong-strain of anti clericalism in England prior to Luther - it was exploited by those early Lutheran converts in England and was a significant point in assisting Henry VIII's break.
It is really important to note that in fact Henry remained devoutly Catholic throughout his life - he had little sympathy for the more extreme reformers - what attracted him to early protestantism was a combition of greed, expediency and ego - like many Prince's he was enamoured of the arguement there were no Pope's in the bible but there were Kings.
4) There is little guarantee that Arthur would not similarily be attracted to the changing thought following Luther. If you look at Scotland where Calvinism spread in spite of a devoutly Catholic monarch and attracted a great deal of popular support that eventually forced significant political change from the bottom up - there is no guarantee that England likewise won't fall subject to the same kind of religious tensions that broke out in England and France later in the 16th Century.
5) Imperialsim and colonization - England's unique protestantism (if you want you can call the high anglicanism of Elizabeth I and James I as catholic light) - played a significant role in colonial enterprise as it upset not only Roman Catholics but many of the rapidly growing more low church protestants - who wanted freedom to express their religion not guaranteed at home - if you remove that you do to a certain extent remove the chances of rapid English colonisation of North America in the 17th C creating a significant change in the way in which North America (the USA and Canada) develops.
6) Parliamentary Monarchy - England remaining Catholic means a Tudor state under Arthur I less heavily relying on Parliament (to reinforce the reformation and amend the succession) - that in turn hinders the growth of Parliament - a monarch not head of the church removes one element of growing discontent with the established church (one cause of the English Civil War). If England remains as a semi absolutist state (which it was in the early 16th century but with a crown reliant on parliament for cash and no standing army) then you rapidly increase the chances of stifling social mobility (reducing the chances of early industrialisation and scientific progress) and increasing royal authority and absolutism.
7) An Arthur surviving reduces the chance of union with Scotland (a significant step in increasing British authority) - for example an Arthur living does not necessarily mean the death of James IV at Flodden - if he survives then the chance of further little Stewarts' being born to Queen Margaret increases despite their poor track record.
8) The succession - a close look at the Tudor family suggests some genetic issue combined with poor health care in limiting the number of healthy issue - fertility wasn't the issue but survival was - Margaret Tudor produced only two surviving children (James V and Margaret Douglas) by her three husbands, Mary Tudor produced only two surviving daughters - both of whom only produced daughters - by her two marriages), Henry VIII managed only three surviving children (all of whom died without issue) from six marriages. A surviving Arthur is not guaranteed any more success in the issue department than his brother.
9) someone mentioned the issue with titles - by Act of Parliament the eldest son of the King was automatically Duke of Cornwall - the title Prince of Wales is not automatic it has to be created by the sovereign for his heir.
Few points that might help.
1) The Anglo-Spanish alliance in OTL was weak and got weaker - largely due to the fact that Catherine's father was quite happy to ignore his English ally (OTL Henry VIII) for his own gain - in fact the first breach came pretty early in Henry VIII's reign much to Catherine's distress. There is no guarantee with Arthur's succession that will change.
2) Throughout the 1510's, 20s and 30s - England would switch positions and alliances as would most of her neighbours - political marriages across Europe rarely resulted in a close long-lasting political alliance between the nations involved.
3) There was a strong-strain of anti clericalism in England prior to Luther - it was exploited by those early Lutheran converts in England and was a significant point in assisting Henry VIII's break.
It is really important to note that in fact Henry remained devoutly Catholic throughout his life - he had little sympathy for the more extreme reformers - what attracted him to early protestantism was a combition of greed, expediency and ego - like many Prince's he was enamoured of the arguement there were no Pope's in the bible but there were Kings.
4) There is little guarantee that Arthur would not similarily be attracted to the changing thought following Luther. If you look at Scotland where Calvinism spread in spite of a devoutly Catholic monarch and attracted a great deal of popular support that eventually forced significant political change from the bottom up - there is no guarantee that England likewise won't fall subject to the same kind of religious tensions that broke out in England and France later in the 16th Century.
5) Imperialsim and colonization - England's unique protestantism (if you want you can call the high anglicanism of Elizabeth I and James I as catholic light) - played a significant role in colonial enterprise as it upset not only Roman Catholics but many of the rapidly growing more low church protestants - who wanted freedom to express their religion not guaranteed at home - if you remove that you do to a certain extent remove the chances of rapid English colonisation of North America in the 17th C creating a significant change in the way in which North America (the USA and Canada) develops.
6) Parliamentary Monarchy - England remaining Catholic means a Tudor state under Arthur I less heavily relying on Parliament (to reinforce the reformation and amend the succession) - that in turn hinders the growth of Parliament - a monarch not head of the church removes one element of growing discontent with the established church (one cause of the English Civil War). If England remains as a semi absolutist state (which it was in the early 16th century but with a crown reliant on parliament for cash and no standing army) then you rapidly increase the chances of stifling social mobility (reducing the chances of early industrialisation and scientific progress) and increasing royal authority and absolutism.
7) An Arthur surviving reduces the chance of union with Scotland (a significant step in increasing British authority) - for example an Arthur living does not necessarily mean the death of James IV at Flodden - if he survives then the chance of further little Stewarts' being born to Queen Margaret increases despite their poor track record.
8) The succession - a close look at the Tudor family suggests some genetic issue combined with poor health care in limiting the number of healthy issue - fertility wasn't the issue but survival was - Margaret Tudor produced only two surviving children (James V and Margaret Douglas) by her three husbands, Mary Tudor produced only two surviving daughters - both of whom only produced daughters - by her two marriages), Henry VIII managed only three surviving children (all of whom died without issue) from six marriages. A surviving Arthur is not guaranteed any more success in the issue department than his brother.
9) someone mentioned the issue with titles - by Act of Parliament the eldest son of the King was automatically Duke of Cornwall - the title Prince of Wales is not automatic it has to be created by the sovereign for his heir.