I haven't read this thread, so some of this might be a repetition.
I wanted to R immediately, but I didn't commit to R for 90 days, and in retrospect I wish I had waited longer, even though R has gone about as well as it can from day 1.
What follows (from here to when I say 'end opinions')is opinion only, filled with generalizations, so you'll have use your own judgment, impaired though it probably is:
It sounds like your H may be stuck in feelings of anger, despair, and fear of what you'll do. It also sounds like his IC isn't doing a great job - s/he should be helping your H process his feelings, not pushing him to decide before he's ready.
I'd like your H - and every BS - to think about what he wants in general and what he wants in his M specifically. I think BSes should remember that 'not cheating again' is just one requirement of many.
BSes should talk with their partners to see if they can agree on what the M will be.
BSes shouldn't agree to R unless the WS agrees to go NC, to be transparent, to be honest, and to enter IC with a goal of changing the thoughts and feelings that allowed them to cheat. BSes should also add their own specific requirements as appropriate - my W agreed to initiate sex sometimes, arrange weekly dates, and write me love letters (which she did rarely, but made up for in other ways - I should take the requirement off the books ).
Some people need longer to decide than others do. When I first started I saw recommendations to take at least 3, 6, and 12 months to decide.
I think it's reasonable for his IC to talk with your H about what will allow him to make a decision. I think it's reasonable for you to talk with your H about what will allow him to make a decision.
I think it may be beneficial for you to ask him if he's thought about rebuilding a new M and what that M would be like.
I think it may be beneficial for you to think about what you want in your M and talk about that with your H. If you paint a picture he likes, he may see a reason to make a decision.
Most of all, I think the quickest way for him to get to the point of making a decision is for him to process his feelings of grief, anger, and fear. Once he's really started doing that, I suspect he can start seeing a healthy future for himself, and that will lead naturally to a decision.
End opinions. For now at least....