I would have thought that whatever is the music policy at the majority of 'soul nights' today is, has evolved due to popular demand. Or else they would fail.
Its the 2 choice option: If you like it - go, if you dont - dont.
I mentioned this before, but just a reminder. In the late 70s and early 80s Northern Soul was not a popular term and got exchanged for Rare Soul in most descriptions of soul nights.
Nostalgia has brought it back, but this time it has become inclusive of all styles, certainly in the main.
In any case, the majority of punters go to soul nights for more than just the music. Its the whole scene that stands out, not just the musical era.
IMO Great soul music has no boundry or limitation, you just know when its good, but at the end of the day its all about personal opinion.
Ed