I love this, especially if it somehow could combine with
@DanMcCollum 's idea.
This is the first time I've heard of Wales being described that way, which is quite a cool idea. Perhaps a joint PoD - an extra daughter, a marriage between a Welsh heir working as the leader of the Varangian Guard, going back to Wales with a new wife and a hefty fortune, and connections to the Imperial Dynasty - and perhaps a portion of the Guard to boot, and uses that to unite the Welsh and establish it in a sort of Neo-Roman/Welsh State focused on unification around the Irish (or would it be Welsh ITTL?) Sea.
Do you have any good stuff I should read on the idea of Wales as the last Vestige of the WRE?
Glad you liked it. I believe I originally read about it in a history magazine some years ago, but I know that Bryan Ward Perkins referred to it in his book The fall of Rome and the end of civilisation (great book, by the way).
I'm going to quote from a fantastic reddit post which I found about this, which sums it up pretty well. But before I do, I really liked your idea of an alliance based around the Irish sea. Efforts were made to that aim, and Robert the Bruce's brother actually invaded Ireland with a Scottish army to help drive out the English in the early 14th century. Definitely worth looking up if you hadn't heard of it. I was surprised to discover this actually happened when I saw a documentary on YouTube about it recently.
"The short answer : Read Britannia Prima - Britain's last Roman province by Roger White and then Edward I, A Great And Terrible King by Marc Morris.
Basically the gist is -
The Romans under Count \Comes Theodosius (father of the Emperor) created buffers of militarised tribes on the Northern and Western frontiers of Britain (Cumbria, Strathclyde and Wales) in the late 4th century before Britain was abandoned after a troubling period of raids by Picts and Irish.
Obviously this was to provide a buffer to protect the demilitarised provinces of what is now England. This is where the Welsh myths of founding kings such as Cynedda come from. So by his logic the early kings the West of Britain were placed there by Imperial Authority. Hence the Roman Draco standard as a symbol of authority (which of course is in its modern form the Welsh Flag though it remained such in many cultures for a long time - Saxons, Bretons and Normans all used Draco standards, see the Beaux tapestry) and the importance of lineage inscriptions on standing stones in Wales as statements of Imperial Authority and rights of Kingship through lineage. They are practically the only prominent inscriptions that we have from the post Roman period which kind of emphasises how important tracing your lineage back to a king who ruled by Roman say-so was.
Interesting note that based on the archaeological record of military belt buckles in the post Roman period the Western Romano Britons used Irish foederati and not Saxons. This also points to the different Roman provinces very much "looking to their own defences" independently and not having a common policy of defence.
Anyway, after the Saxons turn up the Western Romano British Civitate states such as that based around Wroxeter heold out for a while against the Saxons (which is where Ambrosius Aurelianus - Arthur Legend comes in) and while they eventually fell the early British kingdoms of Wales and the North of England held on in some form. Obviously eventually Edward I finally had his way with the annexation of Gwynedd which was the last of them.
Another interesting note is the castle Edward built at the former Roman settlement of Caernarfon (anything with a caer in it or chester denotes Roman Ceaster - castle or fort) which is modelled on the walls of Constantinople. Basically by building an "Imperial - Roman" style castle he was stamping his claim on being the new Imperial authority. There is even an "Eagle Tower".
How important was the idea of Romanness to the "Welsh"? Look into the importance of the poem Breuddwyd Macsen Wledig (The Dream of the Emperor Magnus Maximus) which stands alongside the Gododdin and Mabinogion in the Welsh imagination."
You can find the original post and discussion here:
www.reddit.com%2Fr%2FAskHistorians%2Fcomments%2F3qzzh2%2Fwales_as_the_last_remnant_of_the_roman_empire%2F&psig=AOvVaw2gYG1o8W4JInWLX3f4zT0W&ust=1543534344209871