If I can say my two cents:

1. I preferred that the default behaviour of multi-line was to dedent. But breaking old code, even if for a little percentage of code, IMHO is never a good idea. Py2->Py3 should have proved it.

2. ``` remembers me too much the Markdown for add a code block, not a text block

3. yes, the new prefix is really useless, because it's significant only for multiline strings. Anyway, if this solution is accepted, I propose `t` for `trim`.