I wouldn't have a problem with my fic being used this way since, you know, anything that gets people commenting. It doesn't feel like it's artificially driving people to read, merely to try to say something about something they probably would have read anyway. And even if it did get people to read something they wouldn't read, so what? There's nothing wrong with trying new things.

I suppose some people might have problems because they think the feedback generated is disingenuous... but most fandom fb is disingenuous anyway. People rarely give concrit or say anything that is not perfectly effusive.

As to other themes... maybe holidays? Or if the exchange is holiday specific, maybe holiday cliches? Gift giving, Christmas trees, cooking related disputes, Menorah accidents...