I'm not sure, if I understand this question. ...
Imo it isn't a problem to create this behaviour. It should be relatively easy [1] with combinations of action send message widgets. ... but I think you don't win anything.
If you have a closer look to the toolbar button positions.
in view mode you have:
more edit closein edit mode you have
delete cancel doneTheir position is by design, because it creates a nice workflow.
If you want to save and close a tiddler it needs 2 clicks. .. no mouse move needed, because "done" and "close" buttons share the same position. This workflow is extremely fast and simple.
Similar behaviour is active for the "cancel" / "edit" combination. Nice and simple workflow.
Your toolbar will need to look similar to this:
in view mode you have:
more edit closein edit mode you have
delete cancel done/close doneNow we have 2 done buttons and we have to show them, because if we only show "done/close" button, we will have a lot of support requests. ...
So in my opinion, there is absolutely no win for the core. The core only looses. ... more buttons needed, more complicated workflow, more confusion for new users. ... You only win one click and there is no speedup, since the user needs to make a decision, which "done" button should be clicked. So the new behaviour is only personal taste. Which clearly is plugin territory.
-mario
[1]
http://tiddlywiki.com/#ActionSendMessageWidget:ActionSendMessageWidget%20Messages