To be honest I like the idea you're going about this this, but instead of making
it where you can only have one grab at a time why don't we go with a basic
feature like grip strength. Once a person exceeds a maximum threshold for
grip strength their grip will break. So if you grip with both hands you use up
more of my grip strength and risk losing your grabs, so it would encourage
people to stick to a single grip. I think this could also be easily put into the
current system if you treat the hand like a joint. Put a damage threshold on
the hand as if it were a joint and when it get to a certain amount of pressure
it undoes your grabs automatically.
Though I would rather see this feature put into its own mod, I don't really want
to see the current Aikido mods having this feature in it, I'm rather fond of the
current play style for mods like ABD and would rather not change it up to much,
but seeing features like this in its own standalone grappling/kicking mod would
be very cool.