While the more wholesale appearance change is already available in the game as Ereo said, I think the addition of a Salon is a great idea as it could add a new NPC dynamic in late game during mid game nowadays. Emily is the obvious choice to run the Salon and you'd see Clint there on occasion, maybe even hanging outside the door timidly on occasion. Of course Elliot would be in there every other day, recoiffing and gossiping all the while looking for new inspiration for this next bestseller. Yes, of course Haley too, thumbing through magazines looking for new inspiration about which dresses match her eyes.
So someone will need to be the new barmaid and I vote for Shane. He's already there most of the time, is supposed to be trying to wean himself off the liver-rot, and is out of work after Jojamart is closed. Plus, I bet he looks pretty fine in a maid outfit. So this would be a post-Community Center addition to the game, and IMO not available if the player goes the Joja route. Emily simply will not have the inspiration to open her shop when she sees Joja taking over, and Shane will still have his soulless Joja-job.
However, fitting in a new building into the map might be a problem so it could be simpler to use Emily and Haley's house and just set it up in the entry room. Emily and Haley will need new path-tracing but since both will be involved in the venture, that would be necessary anyway.
I like this, it's a great idea.