actually the ⇥ and ⇧⇥ shortcuts already works
to indent/un-indent list elements (lists, checkboxes). This could
not be applied to normal text because the user could want to use a
real tabulation (the ⇧⇥ could be used but it would be
inconsistent without the counterpart). We will think about the
⌘[ and ⌘].
The commands you are suggesting are very code-editor related. At
the moment there is no plan to adding something like this but I
write down them for future plannings.
I don't really agree with your arguments, you may see how MacDown (
http://macdown.uranusjr.com/) operates, which is one of the most popular
Markdown editors out there. Shift+Tab doesn't cause any problems for