Open source is by far the best developer-focused go-to-market strategy out there. There's no better way for a developer to kick the tires with your project than to just grab the code off of GitHub. Containers and Kubernetes have provided the packaging and the deployment target have made this process extremely easy on both ends.
But don't mistake today's open source for the hobbyist open source. Across the entire ecosystem, open source is increasingly vendor-dominated. Even communities like the Rust programming language are being encroached upon by giants like Amazon.
Many projects are "source available", in the sense that you can view the code, but changes aren't accepted – especially features. As startups grow, they might choose to change their permissive license to something that restricts cloud platforms from copying their code and competing. Companies like Elastic and Redis have done this and continue to do well in the private and public markets. But only cloud providers have a business model that is truly compatible with open source – run more software, any kind of software.
The open source reckoning came for Elastic, when Amazon forked its code and committed to a fully community-led distribution of their search product. Contributors to Amazon's fork can know that the company won't have to trade off commercial interests with what's best for the community. I wonder if the day will come for startups that are aggressively pursuing a go-to-market strategy predicated on openness. Community can be a moat, but open source communities are increasingly scared of the rug being pulled underneath them. Many of these companies can't promise the level of openness they are using to bootstrap. Openness can mean open roadmaps, open governance, and complete neutrality – all of which can make selling a managed service on top difficult.
On the other hand, I think companies like Datadog and Solo have walked the line correctly. I'm not sure exactly what the secret is, but I bet it has to do with setting the right expectations and having consistent community values.