So I hear they're doing Gaim Gaiden for Ryouma and Zack. And while I'm glad that we're getting more Gaim, it does strike me as odd to choose these two. Here's my reasoning, they're both extremes on an one dimensional plane. Ryouma's kind of your mustache-twirling villain. He's mad and he does everything FOR SCIENCE! Making him a sympathetic character would ruin some of that.
Zack is the opposite, he's a mini-Kouta. He's a good guy, but he's never fleshed out as anything other than "a good guy". He's more of an accessory to highlight other characters, like Kaito's leadership skills, or the stand-in for the Beat Riders once things get serious. Not that they couldn't do a good story for him, it's just that he's such a blank slate that could mean anything.
So what do I want? I want Gaim Gaidens for Micchi and Youko. They're both extremely complex characters that are worth diving more into.
Micchi, you're supposed to find him off putting. He's cold, calculating, but his motivations are sort of understandable, if not sympathetic. They could tell a story about how he became the schemer that he is, one about the trials he went through as a traitor, etc. There's a lot of stuff to mine there.
Youko is also a person with a lot of personality, but isn't as fleshed out as much as she could be. We know what she believes in and what she represents, but we could use more background. Why does she want the things she wants? What kind of trials does she face being the person that she was? I think a whole episode devoted to her would be awesome, assuming it wasn't told badly.