That is exactly my thought. If they were to restore cut content, there'd be extra XP to consider.
Moreover, hitting level 20 didn't seem all that special. For one thing, the OC was too easy (I played puppet mode on Very Difficult). They really, really need to implement the IWD death system.
Personally, I would have preferred it if the NPCs didn't automatically level up to your PC's level, when placed in your party. Part of the fun of BG2 was being able to take different NPCs on different quests -- using different quests to level up different characters.
Having a party of mismatched levels just adds more personal flair to the game.
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My apologies if it seems arrogant to assume things about game-making...
But I would also think it's better, economically, to do a TOTSC expansion. Using existing resources to insert areas would be that much easier than designing all-new interiors or tilesets.
Also, many people have expressed their dissatisfaction with the heads and hairstyles. If, to that end, OE added new heads and hairstyles, then most players would probably wish to start over, with a new char...this time with a good head.