This is essentially correct. Trying to be all things to all people massively increased development costs for diminishing returns, and not infrequently forces si

This is essentially correct. Trying to be all things to all people massively increased development costs for diminishing returns, and not infrequently forces significant architectural tradeoffs too. The new databases tend to be narrower, hyper-optimized data model and workload specialists. It requires a small fraction of the code and you know exactly who your target market is. I much prefer this model from an engineering perspective. It is also what drives the interest in database meta-programming scaffolds that can codegen narrowly optimized database engines from something that approximates a specification. It greatly reduces cost/time to market in this new environment. I'm not sure how you would open source a codegen implementation. I don't use any open source inside high-performance implementations myself for good reason, though I occasionally do PostgreSQL mods for companies for fun. Customers care less about open source on the very high-end because vanishingly few people could credibly maintain it in any case.