I asked a very similar question in #6175, eventually phrased like this:
We have a shadowing mechanism, allowing us to use our tiddler in place of another, even though that other one still exists and will be resurrected the minute our own is deleted. Could we do the same thing at the field level?
Jeremy explained that while this is an interesting idea, for some very good reasons, it could not possibly make it to the core.
I noted the following and then dropped the idea. One day I may still come back to it:
Maybe there are enough differences in your current idea and that one that we could achieve it, but I’m doubtful, not without the sort of replacements I mentioned for some core constructs.