A rug pull is when you buy into something and then it's taken away, like when a cryptocurrency token is busted out or you spend money on something and then it's cancelled or nerfed.
Don't like it? Write your own distributed fault tolerant database, or contribute an extension for Raft replication to the Postgres open source code base.
I think investing into integrating a tool into your infrastructure is not exactly "paying $0".
Sole source vendors are really risky, so open source gives a little control back to the buyer that the vendor won't lock them in then screw them later (oracle).
So now if you're paying for Cockroach, you're effectively on proprietary technology with no negotiating levers.
This is why standard APIs, protocols, and languages are a more important thing than specific pieces of software. If there is compatibility you have choice.
Thus it would be up to the the BSL promoters and marketers to decide whether or not this is a rugpull. As an open source user and proponent, I don't really care.
It used to be Apache2. :)
Their blog post announcing this in 2019 happens to now 404:
https://www.cockroachlabs.com/blog/oss-relicensing-cockroach...
But see also: https://news.ycombinator.com/item?id=40058332.
And as you're surely aware, competent OSS contribution is worth thousands