I've said this before, but I think I would have preferred that the 4e Forgotten Realms had been a re-imagining with an emphasis on keeping the basic form and feel of previous iterations of the Realms even if some of the details where changed. That is to say that, for instance, I would have been much more accepting of them just saying Dragonborn had always been there, rather than completely altering the face of the campaign world to justify their inclusion. It would have been a good time to clean up the mess that is continuity by distilling the Realms down to its essential history rather than trying to make it rather than just trying to render it void by shoving it into the far past and pushing the timeline way into the fiture. In trying to justify all the changes they've made, rather than just making them they managed to take the Realms and make them something else that really just doesn't spark my imagination like it used to.
The funny thing is... the Dragonborn were *already* part of the 3E lore (their history and flavour was introduced in 'Dragons of Faerun', I think); it's just that they were the "wrong" kind of Dragonborn, and therefore had to be killed and replaced with the 'Returned Abeir'-stuff. Why not just "retcon" their nature? Or claim that they were warped/altered by the Spellplague to match the 4E lore? Man, they made a lot of weird choices with these changes -- even when there was an easier and more consistent way to do it.