While there is a dedicated forum section for RT/Midi requests, I thought it might be an interesting topic to discuss some of the particular instrumental or MIDI tracks that you feel are under-represented in BIAB. Perhaps it will give some ideas to PGM crew.
Unlike Wishlist, lets try to elaborate on why you feel specific tracks are important. Especially if it's hard to substitute these with other software. I will start.

Non-soloist woodwinds (recorder / flute) rhythm parts that are suitable for genres like Pop / Pop Rock. While there are a lot of brass/wind RTs in BIAB, most are Jazz/Latin or soloist. I think simpler tracks are important because they can be used as fill ins / background for many other genres and compositions outside mainstream Pop/ Rock. Unfortunately pattern/phrase based winds that are available on the market are for either Classical or Scoring music, or their phrases do not transpose properly and have to be used "as recorded". Also, there are almost no musician played MIDI Wind loops / phrases on the whole internet.

Ska, Reggae, Punk guitars.
Simply only a handful of these are in PGM catalog. They are good, but only so few of them. There are plenty of realistic strumming VSTi available. I have tried most of them. Unfortunately these particular genres sound horrible. They need to be played. The only realistic sounding ones are from NI Session Guitarist series, because they are phrase based (similar to PGM) But even if you have whole NI Guitarist catalog, there are only about 8 related sets across electric and acoustic instruments.