I think "Z" you are missing a very important point here. PG is not cleaving a program in two, it is melding two programs together, just what you asked for. BiaB was never intented to be a Full on DAW recording system. It is in PG's not my own words:
"What is Band-in-a-Box?
Band-in-a-Box is an intelligent automatic accompaniment program for your multimedia computer. You can hear and play along to many song ideas and go from “nothing” to “something” in a very short period of time with Band-in-a-Box as your “on demand” backup band."
You on the other hand want a DAW type sequencer to replace cubase in the tool box that is more akin to BiaB which you like but it does not do everything you want or need. You want to take the project from creation to finish in one system. That is why PG developed RB, so you have a choice or either starting in BiaB, and moving over to RB, or just start and finish in RB. The problem is not that the tool does not exist, but the fact that yours does not work.
Again from PG's site: "RealBand is a fully-featured and powerful music arranging, sequencing, and digital recording program. RealBand is a new program that combines the most popular features from PG Music’s PowerTracks Pro Audio and Band-in-a-Box programs into an all-in-one sequencing program with automatic accompaniment."
I look at it this way, if you were building a book case and had a hammer, nails, sand paper, and a hand saw, you could get it done. But to make the job easier, you go out and buy a table saw, a compressor, and air nailer, and a sander, but you have no electricity on the job, those tools are worthless, right?
Rather than complain that the tool maker should take the hand tools, and the power tools, and make you a set of tools that does the job of both without electricity, why not just run an extension cord from a power source and use the right tools.
You need to figure out how to get RB to work for you so you have what you want, not expect PG to abandon their current path just because your system is not working at this moment with their program.
Lastly, You said above all companies do GUI updates, true, but what you are asking is far more than a GUI update, if that was all it is fine. Then it boils down to coming up with a nice face lift. But you want a full rewrite, and actually that has really already happened with RB, you just can not take advantage of it yet. So take another run at it, and let's all see if between Support and the fine folks here, we can get it working for you.
One other thought, take a look over at Cakewalks's Sonar X1 site, folks over there clamored for a big rewrite of Sonar, and they got it!! It has been a nightmare! Bugs galore, Crying and complaining. Actually a rewrite of BiaB to be an all in one program would be far more difficult than the rewrite at Sonar, since BiaB does things no other software can do, and would require a huge project. The way PG approached this to me is brillant. Taking a simple easy to use DAW, and medling in many of the basic features of BiaB, and slowly refining that we have a very handy app it so smart. Baby steps! Keep it as stable as possible. Grow it at a reasonable rate.