First, let me say this: this is just a consideration. It's something that I've been thinking about, but which I don't have a strong opinion on yet.
Since I value y'all's opinions, I thought I'd bring it up here.
The primary reason I'm considering it is that it is beginning to seem likely that a duel of durations may be coming down the pike. And in spell durations, a melee fighter with AMF outdoes damn near any caster... which is exactly backwards of how it should be.
Yes, AMF should scare the bejeezus out of casters... but it can still do that at a 10 min duration or a 1 min/level. And with such a superior duration, it means many casters may not have any good options for running away, either (except fly).
I just noticed that I wrote "round" instead of "minute" in my post above. I meant to write "1 min per level", not "1 round per level" - otherwise, the flat 10 min doesn't make much sense in context, yes?
Anyway, like I said, I'm just soliciting opinions. No decisions are in the works, and likely won't be until this has been discussed thoroughly. Or until, as reapersaurus said, we get to that bridge.