Damn this sucks!
I knew something was up since Mindflayers are CR 8 enemies. But still, 5e was designed for players to reach max level sooner (I have one lvl 20 character on Pnp), so this might mean they'll mess with the progression system.
During the reveal I kinda had the feeling that the exp rewards were very small. I mean a CR 1/2 enemy grants you 100 xp, and those brain things are definitely stronger than goblins.
Well I think there are going to do the same thing as BG1 and BG2 with save importing otherwise it would not make much sense