Ein is more direct and I like that. It's a good character for my brother.
Plus his costumes are legendary (the red trousers, the karaté gi, the leather jacket).
He is not my first choice as a veteran (Leon is), but his presence is appreciated.
I can see his 7P be his CB. Of course, the opponent's reaction wouldn't be the same as before, where he would fly in the opposite direction. His 6P+K is a good option too. The animation would work.
I'm sure there is a way to implant Ein in Hayate's spot for the future installments. You know, to justify his presence and to make sure he will stay forever. A bit like Sheik/Zelda spot in SSBB's character menu. Both share the same space and you can either choose Hayate or Ein during the selection. This would just be an aesthetic justification.
This way, people would stop whining about the fact they are the same character. And Hayate would be a 2-in-1 character (in theory) but they would have two seperate movesets and tiers. I find it more interesting this way.