It may be too late to implement something like this if they weren't already planning to do so, but my ideal solution would be enemy AI that is roleplaying rather than trying to win a video game. By that I mean packs of wild animals that behave like wild animals, goblins that act like goblins, experienced mercenaries that act like experienced mercenaries, etc.
If an experienced sellsword sees a wizard looking fellow muttering and gesturing in the back of the group, I have no problem with him being smart enough to focus on that target. A newborn gnoll on the otherhand shouldn't necessarily be that smart. The problem with all these concentration spells is that the one casting them is almost always being focused down by an AI that is trying to play a game optimally rather than trying to simulate whatever character or creature. If wizard-in-back-fighter-in-front provided the amount of security that you might reasonably expect it to, I don't think it would be such a big deal.
There are certain spells that just shouldn't be concentration based, however, regardless of how the PnP system works. "Protection From Evil and Good" for example is a spell that can only do its thing when you're being attacked, and yet being attacked virtually guarantees you'll lose the spell. Spells like that should really be fire-and-forget, like Mage Armor or False Life.
