Thanks for mentioning this, even though it’s not open source. I wanted to check the business model and pricing, and found the FAQ on pricing refreshing to see. [1] Unfortunately, a $5 per user per month kind of fee may be out of reach for personal use. So I hope the free plan for personal use stays (or they come up with an even cheaper plan).
The free plan for personal use should be here to stay. What's not set in stone yet is whether there will be a Pro plan for more advanced features, and if so, what said advanced features would be (likely cloud services / Kubernetes). But I'd expect the core Docker and Linux machines functionality to stay free.
[1]: https://docs.orbstack.dev/faq#free