That's my beef with it as well... But as long as the mainstream iM@S is still receiving content, I'm not too worried. I'll get iffy around the mobile adaptions when they start meaning less console and handheld releases.
I'm on the same fence, but I'm not too worried about that since Namco Bandai have been doing a good job of balancing out their priorities. Cinderella Girls and Million Live are updated regularly (once every two to three weeks, I believe), but at the same time, the main series is still getting its attention with the recent movie, One for All coming out in a few months, and that PS4 game that's currently in development. When it comes to SideM, I'm more worried about a few of the game's details, like:
-What agency is gonna be represented? Is it gonna be 765Pro again or a brand new agency? Can't be 961Pro, since Jupiter defected from that agency back in 2 and the anime.
I say this because Touma is right there as the sort of poster boy for the game.
-Will it be like Million Live where the game's roster is static or will there be constant new characters added like in Cinderella Girls? Also, will every character have a voice by default or will they have to earn a voice through sheer popularity?
-Will Ryo be in this game in any way, shape, or form!?