For me, and maybe many others, that type of role-play would be in the very "deep end of the pool." I've done plenty of role-play, a few public things, but going down the road to fantasize about an in-law, a friend's wife, a co-worker, etc. and acting on it with a Mistress who looks like the person would be emotionally damaging for some, probably me too. That's why I always resisted suggestions as a young man to do a "stepmother fantasy" with an older Mistress. Just too much emotional baggage. But if you think you can handle it, why not?