Marriage equality means all consenting adults can marry who they wish, or no one can.

I have never heard anyone say heterosexual men should marry a trans girl.

It is not a common position, and has typically has not been extended to mariage yet, but you can easily find articles with interviews of trans people that complain about discrimination because straight cis-gendered people aren't interested in dating them. Some trans people believe that people should accept thier gender in EVERY conceivable aspect of life, not just the ones that don't affect others.

I don't know if Riley has ever said a hetero should marry a trans, but that is the logical conclusion to that argument.

Like I said, I haven't heard anyone say a heterosexual man should marry a trans girl. The logical conclusion to my statement there was that I haven't watched Riley's vid.