Yes this is like solution 1 in that you cannot mix
syntaxes within a
given document whereas solution 2 allows that.
I don't see benefits from being able to mix different syntaxes within
a document so I'd give +1 to solution 1 (with a meta).
In fact I'm not sure to see the advantages of a syntax choice at the
document level (I'd have naturaly put it at the wiki level). Sorry if
it has already been discussed on the list.