We just got a whole bunch of questions migrated from Guitars. As such, I think we need jTab. Many of the imported questions relied on it, and are much worse off now (example). They could be edited, of course, but that would be a lot of work and their quality would suffer. jTab will be useful for new questions as well, of course.
jTab has been enabled here, so the imported questions shouldn't be broken anymore.
(For the related music notation request, we're still evaluating the options there.)