CPIA2002,
I am not sure what poster before me is saying..., but
It was requested before. Many people support Live arranger. Not available yet.

Technically it is possible, but would require very different approach in using RTs. As you might be aware, RTs are not single take of a style played through different chords. There might be 2-3 or more very different takes. BIAB randomizes takes and creates seamless WAV based on your chord progression. If you change something in the arrangement, same "spot" might sound completely different. That is a No no for live arranger purposes for many reasons.

To do a real time arranger, these RTs have to be tailored specifically for live playing. Meaning, they will have to have only single take of entire performance through all the chords it was originally played. And that "single" take would have to be manually crafted to take the best possible bits to compile best performance. That could also be an issue as this is a matter of taste.
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What they could do in the future is take path of hardware arrangers. Introduce Real Drums, some Audio Loops and MIDI for live control, which should not be a huge challenge, as basically it will be a Rompler / Midi arranger and then at a later time add specialized RTs.