So you are saying that if it's $20 more for you to get the new BiaB and would not purchase it, someone else said that they are will to pay 10-15% more.

Now take Tom example, he has owned the program for over 7yrs and has the UltraPak package and pays $469* +15% (Which is $70,35) totals $539.53, my example was for a total of $489. At 10% its $515.90
Believe or not, they do that with Accounting software, accounts payable, accounts receivable and you can pay extra for addins to the software, like billings, fixed assets, payroll, and inventory.
I've even seen something like this for Medical software as well.

Now with BiaB, some people are stating that they would pay for an increase (10-15%) if the GUI and other issues are fixed. I'm only stating, that Any current user should get some kind of discount, and it is possible to separate some of the things in BiaB into addin's (One programming app called them Black Boxes, which are fully capable apps that can can be easily add to an application)

So this can be done, depending on how BiaB is written.
It's as simple as adding their "MegaPAK. UltraPAK, UltraPAK+ or the Audiophile Edition to BiaB, same could be done with some of the components with BiaB currently.

At one time we had Movable/Floating toolbars and they took that away from us. When you purchase BiaB, you get several files in your download, and they are installed by their installer.
There are companies that do this, and they have not gone out of business because of doing this.

As far as how they will do this and what the cost will be, it's not for me or anyone of us to say.