Question for Yamaha.
Do you want to build TOTL for home players, or do you want to build an arranger for professional user who would want to do indepth editing????

You would probably want them to be one thing with one keyboard but that is not even close.
For pro players:
No speakers please.
I don't think we need audio loops, but only if you provide great drums(bfd2,superior drummer,addictive drums)
Same thing with bass and the other tracks
More control when we play live.Not every hall or restaurant/bar is the same.

More modern beats,otherwise you are killing arrangers from inside.

In depth synth engine(more than one)

Sliders or knobs,buttons that you can make it to your liking
better midi editing.
Some of these things are not new,every synth has them for 10-29 years.

I could go on and on with these things.