I did. The signup was completely blank, not even characters selected, no DNWs. There was no letter. Their AO3 had like five bookmarks and no fic. I decided that anyone who gave me so little to go on had to be game for anything and wrote a complete setting change for a fandom that did not lend itself to that.

The recip loved it. Multiple enthusiastic comments, a comment six months later to tell me they were re-reading it.

I think my reasoning was sound. If they had preferences, they'd give you something to go on. If they don't, take your most wild idea and run with it. That way at least you know you'll have fun.