i adore riku. he is my special precious boy.I'm so done with Riku to be honest. Especially when David Gallagher's performance in KHIII was kind of bad. I'd rather Sora in a more fresh scenario than Riku in any scenario.
that being said, i sometimes really feel that the best thing that could happen is for him to get benched. not written out entirely, but at least demoted to a satellite/recurring character a la leon or yen sid. he's a keyblade master? give him an apprentice. relegate him to a teaching role. that way he can still make an appearance and stay connected to the story, but it'd be like keeping him in a cryogenic safety chamber where you don't have to worry about him stealing the show
my biggest fear if he's kept on in the major way that he is now is that something bad is bound to happen. he either dies to save sora (which, to add insult to injury, will probably happen as sora's dying to save kairi, therefore becoming riku dying to save kairi by proxy,) or his character gets ruined (which could happen any number of ways.) i myself would be fine with him being sidelined if it means that his life is preserved and his integrity is intact.