oouuuuuuuhhoouuu what a nice post! let me think about it for a while... in the meantime, if commitment is an opening, how this state of mind allows to enlarge this opening?
The opening doesn't need to be enlarged; the opening is the attack. Think of it this way: if you're facing uke and you're in kamae you're pretty much ready for whatever uke does, this is the point of kamae, you're neutral and uncommitted and so you can attack and defend at will. The moment you move to attack your capacity for defence is gone because you are mentally and physically committed to the attack.
The problem in martial arts is that often the mind is left untrained so when the punch is coming in we get caught up in protecting ourselves and not getting hit and in Aikido terms this means that we get stuck and held at bay unable to make our irimi movement. I don't think I'm saying anything contraversial when I say that without irimi there is no Aikido.
I think that most of the time when we hear about Aikido not working it's not a technical issue, it's a psychological one. It's not a case of enlarging the opening or of needing a commited attack, it's being in state of mind that allows you to enter in when someone is trying to punch you in the face.
Occasionally you see Aikidoka v other arts and you see it where the Aikidoka just stands there while the opponent throws strikes. If the opponent made shomen uchi they would probably stand there too. I'm sure if you put them in an Aikido dojo and tell them to make ikkyo from shomen uchi they enter in before uke can strike. If uke was planning a shomen, cross, jab combination they'd never have a chance to excute it before tori took them down, even if the shomen was short and fast.
If we then take the Aikidoka and throw jodan tsuki at them they have no issue with that either, they're straight in like a shot. Throw a jab at them and they block it, cover up, move back. They have pleanty of time to react and react successfully in that they don't get hit but they react with fear rather than with aggression. So the opening is big enough but Aikidoka are just not psychologically prepared, on the whole, to exploit it.