What if Wessex was not conquered, but was weakened to the point where it was not able to unite Anglo-Saxon England? In other word, Danelaw survives.
Now
that leads to some fascinating possibilities. On Great Britain there would now be, roughly, five powerful areas (some kingdoms, some not).
Wessex
Since it's not been conquered, it's still the top A-S kingdom. It also has the benefit of being under one ruler. The ports of the south-west will still allow good trade, so its economy should be okay.
Danelaw area
Controls a lot of the ports and good agricultural land of OTL England. Powerful militarily, but (IIRC) more dis-united than the idea of 'the Danelaw' might imply.
Wales
Not united under one ruler, but that could change quite easily. Doesn't have the same strong trade links as Wessex, but as it managed to stay independent until the late 13th C OTL, I could see it being a 'power' in this scenario. Depending on how weakened Wessex is, it might even be possible for it to expand a bit to the east / north-east into what was Mercia.
Alba/Scotland
Recently united, from the kingdoms of Dalriada, Alba and Strathclyde. Probably the second power on Great Britain after the Danes (in this scenario where Wessex has been weakened). Could easily take advantage of infighting in the northern Danelaw to expand to the south. Northumbria could easily become part of TTL Scotland, though I think it would struggle to go any further than that - so maybe down to Westmorland in the west and the Humber in the east. However, with those lands it would be richer than OTL, with more good agricultural land and more ports for trade.
Kingdom of Mann and the Isles (or whatever we want to call it - the north-western Vikings)
If Scotland's focus goes south, then that gives the Norse in the north-west time to consolidate. If they can avoid infighting, then a more long-lasting kingdom might be possible here too. If those who control Dublin and other parts of Ireland could be united into this kingdom too, they'd be a power to be reckoned with.
Thoughts?