If I were using something like Band In A Box, I'd probably be creating my own arrangements with it and then playing along. I don't tend to do things like everyone else, tending to pair songs together that may not have been paired previously, taking off onto little side trips where I might play a part of a different song in place of the current one where the chord structure works just fine, but it's unexpected, sometimes even a bit humorous or playful. I'd probably not be that interested in off-the-shelf tracks to play along with.
I do kinda remember a friend, years ago, that had a Yamaha keyboard that would do some little tricks like play along with bass? or drums? and had a few quick "buttons" of some kind that he could quickly generate a 2 bar? or 4 bar? ending. Not even sure what that would have been. I recall it being pretty simple, not really able to handle complex chord structures, that kind of thing. Certain kinds of music it might work better with than others. Probably not so great with jazz.
Anyway, I haven't exactly seen setups that were geared towards flexible live performance, usually more geared towards laying down some decent sounding studio tracks. And I suppose that's nice. Maybe not quite what I'd ultimately hoped to find. Never know, with AI so commonplace in music these days, it may not be that far off that AI could be a person's backup band, live, impromptu. Guess we'll see.