Ah, Open Source
I still don't really understand these arguments. You started Open Source, free for all. Now that you have business people telling you that you can make mint out of that code, you're switching allegiance.
That feels more than a bit like a bait-and-switch to me. I'm pretty sure that, if their code had not garnered interest outside of the ham radio community (just an example), they wouldn't have bothered.
But no, they started Open Source so everyone could benefit and marvel at all they could do with the code, and now that they're successful, oh, hey, you should pay now.
I think there needs to be some honesty in the Open Source realm, as in new projects should clearly state if their intention is to monetize and change licenses down the line.
And, in any case, I don't think it is fair to put a blanket change on the code. You want to change license ? Fine. State that, as of YYYY/MM/DD, the last version under Open Source is the current NN.XXX.ZZZZ-WWWW (version numbers are such a hassle these days), and as of version BB.FFFF, the license changes to pay as you go (or whatever).
That would be more honest for everyone, and much less hypocritical for the company.
The other solution, of course, is to always be wary of a company offering code as Open Source. You just know that, if they become successful, they're going to change. For the worst (as far Open Source is concerned).