If they were going to apply the RAW for spells per turn, it should be across the board, not just for the Sorc using Metamagic. A cleric can still cast two healing spells per round, a wizard can misty step and fireball in one round, so to prohibit a Sorc from using two leveled spells with Metamagic when other classes can normally cast two leveled spells effectively penalizes the Sorc for using a class ability, and that would suck.
That being said, I don't mind this rule change, I think allowing more than 1 leveled spell per turn makes for more interesting options (and faster spell slot usage), a positive so long as combat encounters are designed accordingly.
Rather, the fight project shouldn't be a problem. So far Larian is doing very well in this respect (it would be better with the difficulty levels, but what to do, you have to wait).
One metamagic is unlikely to significantly spoil the game, especially as you said any class can.
This means that the game will be specially designed with the possibility of casting additional spells.
There is also no need to worry in advance that enemy sorcerers will be able to destroy the team during the turn.
It is unlikely that Larian will allow them to cast any spells using metamagic. Another thing is that npc doesn't obey class constraints anyway, so that's even less of a problem.
