IMO, not only can Ravenloft be easily converted to 4E, but from the sound of it, 4E will be much better suited to running a Ravenloft game then 3E ever was.
for instance, the books have made it clear that spells were memorized
That's not a big deal. The books have also gone into detail about Drow Infravision, and yet they switched out Infravision for Darkvision without any problem.
specialist schools of magic exist (Strahd's background contains extensive info on the necromancy school and how he got into it).
There'll be a Necromancer class. And Strahd's a case of how 4E will be good to Ravenloft. For instance, he's always been described as a powerful warrior. However, when he's statted out, he's just a 4th-Level Fighter. With retraining rules, one could have a Strahd who was a 16th-Level Fighter at the height of the war with the Tergs, but who then, through retraining, started to lose those Fighter levels in lieu of Necromancer levels.
In addition, Necromancers made for pretty poor Necromancers. Clerics did a better job of that then Specialist Wizards. With Necromancer becoming its own base class, it'll doubtless become MUCH better at what it's supposed to do. Namely animating and controlling undead.
There are no dragonborn or tieflings.
There are no Half-Orcs, either. This was easily solved by making them Calibans in Ravenloft. Same thing can be done, here. With Calibans being treated as either Dragonborn or Tieflings, mechanically speaking.
Paladins in ravenloft were only lawful good.
Elena Faithhold.
Besides, in 2E, only humans could be Paladins. There was no need to rewrite the setting to explain the existence of non-human Paladins when 3E came out. Likewise, there's no need to rewrite the setting to explain the existence of Paladins who aren't Lawful Good.