I’ve thought about this too on numerous occasions, and I’d say that yes I believe they can work, I don’t see anytning wrong with the author wanting to put a piece of themselves into their own work afterall. I feel it’s about representation, in the same way that you write a story to better represent what you want to see story wise. I know that most stories have the MC as a self insert but writing your own story and writing a self insert as an NPC feels different, there’s more room to add detail I feel.
I did mention in another post about RO’s with ties to the main plot overshadowing the MC, as long as that kind of thing is avoided so the reader can still feel as if they are experiencing the story from the perspective of themselves and are not from the perspective of an insert of the author, which I could suppose is always present in choice of games to an extent and with varying degrees.
I totally understand wanting to have a character that is “yours” or “you” in a piece of fiction you create where the MC isn’t, from the perspective of a writer anyways. So, I’d definitely think they can work if certain rules are adhered to and if you wanted to write one into your story I’d say go for it, it’s your story after all, to do with as you will. 