Most ATLUS games are only released for a single platform anyway. Sure, they hit a variety of them. But if you're a Persona fan, you need the Sony systems. No way around that. If you like the Devil Survivor games, you need a DS. Etcetera. ATLUS doesn't do multi-platform releases of a single title.
Personally, I'm pretty dang unhappy with this. SEGA does not have a good history with me. They were once a beacon of the industry. They then drove their own consoles into the ground, forcing themselves to switch to software only. Their history with Sonic Team shows just how badly they can ruin a good series, and how far they'll go milking it. And their recent history away from Japan has been horrible, in my mind. They butchered their own US distribution centers and localization teams, and they've refused to localize most of their niche titles, like Yakuza and Valkyria Chronicles.
I'm afraid that ATLUS America is not going to survive this acquisition, and that we'll never see another Persona game released stateside.