In 5e, they also have some spells that require concentration, but rather than requiring your standard action (or whatever action you've mitigated it to), it is simply a status of "I am concentrating on a spell, so I can't cast another concentration spell."
It seems surprisingly elegant.
Although it does have the direct effect of only ever using the best concentration spell at once.... because you can only use one. But a buff to attack is circumstantially different from a buff to ... something not combat related. So there's still analysis and decision making. Plus, that comparison already happens between spells, because you can generally only cast one per turn, with hour-long spells being notable for not jockeying for your actions, and not being limited any basically any way, so long as you believe you are not going to run into an anti-magic f- well, so much for that.

Anyway, before I continue rambling, I was wondering what you guys would think of that system, if it were backported?
Obviously, in 3.5 concentration spells were (hopefully) designed such that they were worth spending the action on. So it probably wouldn't be a smooth port. Especially if you're going to need to go through 1,000 spells just for the core classes' first level spells and see if they need any adjustment... eh. Know what? Screw that.