Bugger, lost my first version with a careless touch to the wrong part of the screen. Wouldn't have happened on a laptop! Once more with feeling:
I second and +1 this one, as it affects me greatly, as I make a lot of use of these in work-related docs, and it was immediately apparent even on the very first document I happened to load up to play with in my newly-bought Editorial.
With Multimarkdown selected in settings, I believe 3-backticks-style fenced code blocks should work and don't. I think they're just being interpreted as inline-code. This, plus the fact that the indented-block method does work, can give at least some of the odd effects we see; as for example, as soon as there's a blank line followed by something indented, the code block finally starts, and when there's another blank line followed by a non-indented line, it turns off again. You can imagine the mess this makes of pasted bits of source code.
It would be easier to deal with at least if I could find a way to indent or outdent multiple lines in Editorial (like splat-[ and splat-] in Sublime Text for instance), but otoh... I use fenced blocks because doing that indenting on everything I want to paste in is too much effort even in Sublime Text.
Fenced code blocks are right there in the Multimarkdown cheat sheet here; so while they're often described as "github-style" (because they are, relative to plain markdown), they are expected functionality for a multimarkdown settings switch too. :-) Syntax colouring would be a nice-to-have there, but it actually producing a code block at all where it should is a must. :-)
Otherwise, it's all looking very promising. :-)