It is the audience and landlord who will ultimately determine the future of any session. I have seen sessions die out because a small elite exclusive core will dominate with a very narrow range of musical tolerance. Eventually people vote with their feet and the landlord terminates any agreement. These sort of sessions should be held in a seperate closed room if the music played is for the players benefit alone!

The ideal session will usually have a theme Irish, English, whatever but will also be tolerant of other styles. Audiences may be noisy but if it's in the main bar then this is part of the experience. However if it is in a seperate bar wher the audience pay a fee then noise during a performance is unacceptable.