Gaidens, or Paralogues as we call them now, are pretty sensible in Three Houses. In fact I'm surprised they weren't done this way long ago. They're entirely side character focused and unlocked simply by having a character, or multiple characters alive and unlocked in your army by a certain point in the game (supports might also play a role, not sure). Gaidens in Shadow Dragon on the other hand are highly critisized because they require killing over half your army to access. And the Gaidens thems
I'll put in my ideas for gaidens, assuming none of the new content that actually got into Shadow Dragon exists (trying hard not to rip off @TriforceP's ideas because I really like all of them). They've mostly all ended up being in the same place as the actual gaidens in the game, but that's because those generally are the best opportunities to have a Gaiden chapter in the story. Like in Three Houses, the player will be given the option if they actually want to embark on these quests, as all the