Jammer is great if you want to stay purely MIDI, but I wouldn't say BIAB has stopped work on their MIDI functions. In fact, one of their new features is "SuperTracks," which are MIDI files played by musicians. I guess they were listening to customers who wanted both the realism of the audio RealTracks and the control and tweakability of MIDI files.
BIAB has always been able to generate MIDI versions of tracks, but these were generally limited to the basic backing parts, i.e. you won't find a Brent Mason-played MIDI solo (yet), but this is changing now. John Jarvis plays on the piano SuperTracks, for example.
The drawback with RealTracks, as good as they are (and they ARE good -- I doubt you'd be able to duplicate those Paul Franklin pedal steel parts in MIDI) has been that the same exact licks you might use in your song could also be used in songs by any other BIAB user. With MIDI SuperTracks, you can customize to your heart's content.
For someone deciding between BIAB and Jammer, the key factor (other than cost) is how good your sampler capability is. BIAB will supply pro-sounding audio tracks, no sampler needed. If you're a MIDI maven with Kontakt and a bunch of high-quality libraries, Jammer is probably your best bet. I hope this helps!
Cheers,
Eddie