To weigh in on the proposals:
(1) (single-digit start numbers) seems okay to me. It might fix some
practical problems (and might cause some others). On the other hand,
even with this fix we’d have a mismatch between parser behavior and the
spec of the sort described in commonmark/cmark#204.
(3) is bad for the reason I just gave in my previous post.
One-item lists are, in general, useful, so we don’t want to
rule them out altogether. I suppose we could require at least
two items when the list interrupts a paragraph, but that creates
difficulties for parsing: you can’t know you’ve got a list until
you’ve parsed the whole list item and seen what comes after it.
(4) has a similar issue: we can’t tell if the list is going
to be loose unless we’ve parsed the whole thing. And I’m not
sure what is gained by allowing only tight lists to interrupt
a paragraph.
(5) is going to be problematic for people who wrap their text
to a reasonable width (say, 72 characters), and also for people
who don’t hard-wrap at all. And I echo @mity’s worry about surprising
behavior.
(2) seems the most promising to me, but there is the worry
about languages with different punctuation conventions.
I guess it might be a good idea at this point if someone
summarized clearly and concisely why we need to change things.
My own intervention above was motivated by
Bug in lazy blockquote continuation (or corresponding spec is wrong, whichever) · Issue #204 · commonmark/cmark · GitHub, but I believe
that issue could be handled at the implementation level without
a change in the spec. At any rate, I’ve written a Haskell
implementation, roughly following the same strategy as cmark,
which gives the right results in this case.