It’s true that disallowing lazy continuations would simplify creation of parsers. But we have parsers now that handle these things efficiently, and a spec that defines behavior even for crazy things like the above example. (I guarantee that if you eliminated laziness you’d have howls of protest.) Having just one bullet list marker or thematic break style would not simplify the spec or parsers significantly.
I have already put down my thoughts about how some tweaks to Markdown syntax would create a more rational language and simplify the spec and parsers:
and with slight modifications at