Your incentives aren't aligned with the community. Should a free, open-source alternative to Lunar exist with all its features, your sales would go down. It is in your best interest to:
1. Create the best possible product that works the fastest, smoothest, without bugs, etc.
2. Create a minimal viable free product maximizing the amount of new trial users for Lunar.
3. Maximize the difference between the free and premium product to convert the most users from #2.
Open source contributors shares incentive #1 with you. They don't share incentive #2, but there's no conflict here. But incentive #3 directly clashes with those of an open source contributor if only the free product is open source.I want to assume good intentions here, because the malicious interpretation would be that one wants to take advantage of the open source community by getting free work done on incentive #1 while rejecting anything that would cross incentive #3.
So what is your goal? You obviously want to make money - we all do. What else? Is your goal to give to the open-source community for similar applications that wouldn't directly compete with you? It's noble, but risky, as you can't enforce that. If your goal is to conduct a 'business transaction' with the open-source community: "access to my source code in exchange for potential contributions under conditions w.r.t. incentive #3", that's fine too. But that is not open-source.
If you simply publish the source code explicitly stating that parts of the source code of Lunar is available under a permissive license, that you only merge contributions that fix bugs or add pre-approved features, but otherwise people are free to do with it what they want, I don't have a problem with it. But calling it open-source is misleading in my opinion.