Reading the comments here, it seems to me that there are two sides to the debate: One side says it's not FOSS unless it's completely free, and the other side says it's fine for a small subset of use cases to lose a modicum of freedom if it means that everyone else benefits with more software that's essentially OSS.
I think that what the "purist" view is not considering so much is that, when it comes to a company like Timescale, the choice isn't between "OSI" and "source available", it's between "source available" and "closed source". They're a company that wants to make a profit from the software it spends resources to develop. The debate seems to be mostly on whether this license should be called "open source", but I think there's an implicit value judgement there, which I'd like to make explicit.
I'd like to clarify that, given that it's almost impossible to make money when AWS can just take your OSS product and undercut you, Timescale is doing us all a great service by giving us a product for free and making the source available. However, does it really make sense to argue over the license is OSS or not?
The FOSS ecosystem has a monetization problem, and it's largely being funded by our collective donation of our time. I think that having options that allow us to grow the ecosystem in a sustainable way is important, even if they aren't as pure as we'd all like. Practicality usually beats purity, and "source available" is better than "closed source".
I haven't really seen any concrete dangers that come from a "source available" license, especially any that make it worse than just having no source (which is the real alternative here), so if anyone could educate me, I would be grateful.