Nick_ - I've already PM-ed you with my initial thoughts.
This could be a winner, if handled right.

That end of Yorkshire desperately needs a quality-singer-friendly session night at a weekend (Friday or Saturday), in a suitably decent venue (ie at least reasonable acoustics and sufficiently away from a smoky noisy bar area).
Guest, Grazzer - there are already venues catering for the niche-markets of the "concert" audiences, the musician-sessioneers and the acoustic-singer-songwriter brigade.
Me, I would travel from the other end of the county for a good sing with like-minded folk in convivial surroundings - and I do, if there's the right supportive atmosphere..
And I'm sure there's many fellow Catters who feel the same.