I’d like to add one more option: Make Grin more softfork-ready. This isn’t foolproof, since it’s difficult to predict exactly what changes may be desired in the future. But there’s a few things we can do that will provide a decent bit of flexibility.
Making Grin mode softfork-ready is something that can be researched and proposed in parallel to this discussion. I think it would be important to understand what changes we would like to see there, regardless of the options above. Would you agree?