I can recall watching several relatively recent live shows, all on NBC. There was the special presentation of Fail-Safe, and episode of ER, and an episode of 30 Rock. I had no interest in watching The Sound of Music, nor the Hot in Cleveland episode, nor will I watch Peter Pan.
While the gimmick factor of a live sitcom is intriguing, I fear that what will end up happening is that it will turn out to be a boring show along the lines of Sean Saves the World, or one of the peacocks other equally lame attempts to recapture the magic of the days of "Must See TV". Doing a sitcom live won't make a badly scripted and/or acted show suddenly watchable. And, if the show is really good, it won't need the gimmick of being live to make a difference.
However, there is a genre of TV program that's been missing for a long, long time, aside from one poorly done attempt recently. The old-school musical/comedy variety show could be ready for a comeback. And doing that kind of show live could make a big difference in the show. Saturday Night Live has given NBC a wealth of experience at cranking out a live TV show. Now, they just have to find a cast and some writers who are actually entertaining, and good enough for prime time. Within the context of such a variety show, a recurring sitcom skit might be a good thing to include.