I'd recommend taking it slow, but maybe he's learned what he needs to make this work. I've seen it in my own family where it took several attempts for them all to get it right, but once they did, their marriages have lasted.
I know a guy that lived with his wife for 7 years before they got married, and they have 2 nice kids. I know another guy that lived with his wife for 12 years before tying the knot.
Rush needs to check out their plan as far as a trial run is concerned.