Earlier quoted context omitted.
Cession of eastern territories and Crimea is probably not going to be too difficult a decision, considering Russia controls them anyways and did so even before the war. Demilitarization of Ukraine, NATO membership and relations with the west in general are all going to be very contentious, and it's hard to see a solution here that both sides will accept.
Demilitarisation is an absolute non-starter, I don't see how any sovereign nation could ever agree to that. I assume Russia are putting it on the table so it can be traded away for something else. If what you say is true about Ukraine being willing to trade away Crimea and the eastern territories, then I don't think an agreement is necessarily that far away. Your initial demands in a negotiation are rarely your red l…
Particularly one next to Russia. (And Ukraine, in particular, after this?!?)
The Chutzpa negotiation approach would of course be, "OK, let's discuss demilitarisation. How and when do you propose to start yours?"