Diogenesister, you're right about mainstream churches at least being more noticeable in the community. In the town where I live there are a bunch of old churches with pipe organs. Last year they organised an "organ crawl", an afternoon where each church would be open at a certain time and an organist or two would play a piece or two on the organ before moving on to the next church, the audience moving on with them. I was too crook (sick) that year to attend, unfortunately.
Recently one of the churches allowed the organist to play a piece she had been learning, Bach's Passacaglia, at the end of the service. It was very moving. 😢
I can't see the WT opening up to outsiders in similar ways. "Brother Jones Solos the Latest WT Christmas Carol*" probably doesn't have much pulling power, and besides, the WT probably doesn't have the insurance to cover such events.
* https://www.jehovahs-witness.com/topic/4864613443698688/org-came-out-christmas-song