I think the common bottleneck on both of your proposals is fleshing out use-cases.
In principle, I’m for maximum sighash flexibility: anyone should be able to elect to include any component in their sigmsg. But the reality is that there will be some limitation on that interface - bitmask/template parameters can only be so long, and different approaches merit different caching strategies.
To resolve this, we need to have a clear idea of what the proposed uses are - that is, what are the use-cases are not met by the standard 119 template hash? Ideally, you’d both be able to present some kind of code sketch of how these use-cases are satisfied by your proposals.
The details that you’re discussing above are worth discussing, but I think they are dwarfed in comparison to the thing that’s blocking the evaluation of both of your proposals, which is: what exactly do we need different sighash/template modes for?
Emphasis on exactly! 