I've never done this exchange and am probably not going to this time either because it just feels too intimidating somehow, but if I was going to, the canons I would request wouldn't necessarily be the ones whose worldbuilding I love. Like, The Expanse is a canon with a lot of worldbuilding I love, but it's not one I'd be likely to request in an exchange like this because I'm largely satisfied with what canon gave me on that front. I'd probably request stuff like Star Trek or the MCU, big sprawling canons with a lot of different things going on that weren't all explored very much. Like the time Star Trek Discovery set up this whole thing about Saru going back to his home planet nine hundred years in the future when it presumably would be massively different, and then did very little with it. Or the time Star Trek Picard set up this whole thing about an ex-Borg rehabilitation project and then did very little with it. Etc.

What I probably am going to sign up for is Space Swap, and request a couple of worldbuilding tags along with a bunch of character and relationship ones. I'm also considering Hurt/Comfort or maybe Id Pro Quo but I'm not sure exactly what I'd want to request this time.