(FWIW, 10k mobile push notifications a month sounds high, but it is not a very high limit; in practice, a lot of teams of fewer than 25 users exceed it.)
I will say that we put a lot of careful design and engineering effort into doing this transition in a way that cannot result in unpleasant surprises like upgrading to the latest release breaking a feature you're relying on.
Using a 100% open source product provides customers with a lot of protection against bad behavior by vendors. If you're using a proprietary product (including the paid/proprietary versions of open core products that market themselves as open source), the vendor has a huge amount of power to move a feature you need to their Enterprise plan that costs 5x as much, and if they do that, you're stuck either running an old version (which will accumulate serious known security vulnerabilities), upgrading and dealing with the changes, or migrating to an alternative, which in situations where the product has all your data in it, can easily cost far more in than the product itself.
I can't say I have all the answers for how commercial open source software should work. I can tell you that open core is a much easier business model.
The hope is that people do care about the very significant benefits that come with using well-engineered, no tricks, 100% open source software, and that businesses that are relying on open-source software are willing to pay for the services and support that they need to succeed with it. Time will tell.