I haven't seen a mod that changes vanilla Taverns in that way, but there are mods out there, which have such Taverns included. For example: part of the mod 'Shezrie's Towns' is the small village of 'Heaven Bay', which has it's own Tavern. Inside I have found two Musicians, playing a lovely sound, and always between four and six dancers. Because I take a lot of screenshots, this place gives a nice background for my pictures. Still have to find out, of the other Towns from this mod have similar additions.
So far the tavern in Haven Bay in Shezrie's Towns has the musicians, dancers and music. That tavern is pretty much the template for what will happen to all 6 bars in Shezrie's Towns as soon as I can find music.
In Pell's Gate, The Roaming Spirits Inn has very nice music but I thought a bit too small to put in dancers. The Cloak n' Dagger tavern has background noise and is packed with interesting people. The Royal Hotel has background hotel type music and the cafe and shopping area in the Gallery has music too.
My biggest problem is finding suitable, non copywrite music and that is why I haven't dived into bringing more life to the Ravenview Village, Woodland Village and Lakewood Village taverns. So if anyone knows where there is some medieval non copywrite music I would be really grateful.