If I was to tweak concentration rules I would probably do it through feats which allow you to concentrate on more than 1 spell at a time, with a downside which makes it dramatically easier to fail if something tries to interrupt your concentration.
I would do this, too, but not as a feat. I'd just let anyone concentrate on two things, at a +5 to the DC of Concentration saves, or three things, at a +10 to the DC. And if you fail a Concentration save, you lose ALL the spells you're concentrating on.
