Ahhh…I had a whole bunch of stupid text here (now deleted) because like an idiot, I only read what you wrote and didn't try it out.
So, adding at the end of the line worked as expected.
When I tried adding a backslash + space, it didn't: a backslash appeared beneath my image. But when I typed just the backslash, a weird character appeared (don't know what to call it, but it looks like backwards L on its side.
Doing that worked too, and typing "\" is must faster than typing " ".
As a wise man said, "All you can do is all you can do."
This workaround makes it SO much easier than what I was going to do, and I completely agree with the choices you made for MultiMarkdown 3!
As far as I'm concerned, the workaround is good enough that I have no problem waiting for this to come off the back burner in the distant future. I suspect there could be formatting challenges if space is tight (tables come to mind), but as you say, "One thing at a time."
I have another suggestion if it's not too awful. I make that after our team stand up. :-)