In reply to Peter Knight.

how so?

How exactly are you going to resolve merge conflicts? hmm sorry... how will you even know there is one? Take for example one changeset that sets the text color to white and another that sets the background to white. Each one of the changes might look ok when tested, but together the results in an unreadable site.

The whole changeset idea is parallel to reality. In reality every code change like theme or plugin update will need to result in nullifying changes set because you have no idea what would be the impact of combining the changeset with the new code.

I can see some use case for people that might get interrupted while making big amount of changes, but how often that happens? almost never?

This is totally plugin territory, and the bloat do not have to be inflicted on the 99% of wordpress users that will not even understand the idea behind changesets.