Upgrading Existing Lightning Channels

I guess the question I have is whether or not people want to see DynComms broken up into two proposals: the part with the funding output conversion, and the part without. I think we are amenable to breaking up the text into separate documents or per your suggestion maybe just different PRs into the same document if they are sharing a negotiation process.

If breaking it up means we can get better prioritization from Eclair/CLN/LDK for the ability to change the state-space constraints and the commitment rendering function, we are happy to do so. Being able to reuse DynComms for TRUC commitments seems like a very natural evolution to me.

CC @t-bast @rustyrussell @MattCorallo