My view is we should argue for a solution or enhancement and leave the core compatibility question to later in the discussion, sure if you specifically want to rewrite something it may need to be listed for a later major version but most of the time we can find a solution that is also backward compatible.
There are so many ways to enhance or hack tiddlywiki already. I would argue that as it matures such drastic rewrites will become less common.
- Just start with asking the community
- A question such as * Should caption be displayed as main title? - Discussion - Talk TW (tiddlywiki.org) already has the answer yes, just hack it.
- Even substantial refactoring or UI alternatives can be implemented on top of tiddlywiki already and you can release your own custom Edition?