Total shot in the dark, but what if instead just filling in for Philip the Fang Memory/Gadget actually holds whatever remains of him? That way it could lead to a push in the story to actually figuring out the mystery behind Philip and the Gaia Memories. But in regards to the second rider is it just me or does anyone get the feeling that he is going to end up doing the whole complex calculation gimmick as his finisher.
And on a more tangential note, does anyone want Kirihiko/Nazca to end up being an evil rider, I mean his obsessive nature towards Double could drive him to trying to become a rider. Also that increase in power (provided by a pure Gaia Memory) could allow him to beat the Sonozakis.