I would agree with
@jingleballsie in that I've encountered any that I could think of. There are some tropes that I would like to see more of because the ones I have seen aren't that great or there are few of. An example of this are the mom teaching the son about sex. I also like when the mom and son pretend to be a couple and end up doing things. One of the best in this trope IMHO is SpacerX's
Dating Maggie although the mom and son never have sex in that story which is a waste. Still a hot story, but it needed them to have sex at some point.
There are other tropes that I'm not thinking of at the moment.