One experiment that was tried a few years ago at the Brantford Folk Club (Ontario) was to put 3 solo performers on stage at once and have them take turns presenting their mini-sets. The idea was that it would save time on set-up (we used a full sound setup) and turnover. The neat bonus was that sometimes the performers would collaborate on each others songs and take the performance to a new level. I loved it, but the experiment was fairly short-lived for some reason.