Uli posted only a couple of days ago that they will add a feedback eliminator into the xr18. While not mentioned this most likley will enter the x32 as well by my guess.
And possibly more to the point, chances of an "out of nowhere" feedback that is loud enough to require split second fixing *should* be pretty remote. Most feedback issues manifest themselves right away when you bring up the system (because a knob got changed while taking down or setting up or something got mispatched) or when a change is introduced in a previously stable system (big hat, sunglasses, different performer). For a band running its own sound from stage I can't picture personnel or wardrobe changes that the band and mixerperson would be unaware of. Unless the band is going from the trailer to "live, right freakin' NOW!" I'd think 90% of the feedback would be caught during the line check at setup.
This does, of course, presume that your systems, main and mons, were set correctly to start with. If not, you need more than fast access and a feedback eliminator...