Mamoru should resemble the anime or manga Mamoru, or else one isn't
writing about Mamoru, one is writing about some other character entirely
named Mamoru.  The same applies to any of the other characters.  While
there's always room for interpretation, one can reach a point where the
characters are no longer recongizible in behavior.

I must agree there. While I wasn't disturbed to see a completely
different future Endymion (things can happen in about a thousands
years), I've been very bothered by the caracterisation of Mamoru.
Having him asking Usagi's Hand because of the dream is in line with the
personnage. The fact that he is, already, somebody prone to very violent
reactions against loved ones isn't. Another thing that I find hard to
believe is that none of the people who know what he can become will tell
him. From the moment he knows about the existence of Chibi-Usa, it
doesn't make sence. I would at least expect somekind of explanation from
Usagi, who first of all, would want to change the future.

Well those were my two cents...