I have to wonder: does B4x support plugins?
B4x users might be more hesitant to pay for something, but on the other hand there are many more of them. So would MBS for B4x be possible?
We call it libraries in B4X and most are even Open Source. Unlike with Xojo, there are hundreds of library builders. I’m not sure there is real money to make with them, as, even you write a commercial one, chances are there is an open source one too. But then again, maybe with the support that MBS delivers, pro-users may be inclined more to pay something for them (not in the $1000 range I’m afraid).
B4X chooses the path of Open Source more and more as Erel believes this is the future of dev tools. Even almost all ‘official’ libraries have now their source code on Github. And for the ones not yet on it, just ask Erel and he will most likely provide it. 
btw, has your 400.000 users ‘income calculations’ post been deleted from the TOF? I don’t seem to be able to find it anymore…
Yes. Not unexpected.