And now for the bad part...
Shouldn't Alter be rigged on Ike and normal Saber on Marth? In particular, Alter would follow the typical "stronger yet slower" aspect of most evil variations, like how she is in Unlimited Codes. EDIT: Apparently this is already being done. Nevermind then!
Secondly, I believe the size-mod for Archer is borked. The screenshot below shows the size-mod version next to the normal version. As you can see, they look exactly the same - to the point that I don't even remember which one is which:

Thirdly and least importantly, Rider rigged over Sheik NEEDS to happen.

Caster also would be a perfect fit for Zelda (even has pointy ears!), but I'm guessing that's lower priority since Rin's already rigged on Zelda. Assassin (non-true) would also be nearly a perfect fit for Marth, and I think Kotomine fits very well with Captain Falcon's fast-yet-not-fast-but-powerful attack style.
Other characters that could work well are Lancer on Marth, Gilgamesh on Ike, Berserker on Ganondorf, Kotomine on Captain Falcon, Kuzuki on Captain Falson, Shirou on Link (since Archer's on Pit), Sakura & Dark Sakura on Zelda, Bazette on Sheik, and... I think that's it in terms of what may actually work.