Oli,
That was also discussed same as a possible JSR, but you see with the Config or MVC efforts, that both cause difficulties being used by other Jakarta EE specs.
Mike stated here, that MP libraries may not be used by other specs for IP and compatibility reasons.
JNoSQL and Jakarta NoSQL are both where Hibernate or TopLink used to be around 2001. A lot has changed there, but after Jboss hired Gavin and others they worked full time on it. Currently while Jakarta NoSQL is already used in production by a few companies, there is no full time developer like that, neither Otavio, nor others. As long as vendors don't get more involved, it may be slower than Hibernat and JPA, but while the Spring Framework uses that a lot, Hibernate was never merged into Spring itself either. Nor does the abstraction over multiple NoSQL paradigms and approaches belong to Microprofile.
MP gathers patterns and best practices for Microservice development, a bit like Spring did from 2002 or 2003 on.
Despite the fast version change driven entirely by PR folks in a few companies, it is on the level of Spring 1.2 rather than 2.0 at most. Do you think any Microprofile part has been downloaded over a Million times like Spring until 2.0?
I don't think so, thus it's evolution can be seen at a ore 2.0 Spring level now, even though the industry is more diverse now than 15+ years ago.
There are other NoSQL efforts at Eclipse, Vert.x or Jetty, but all I saw the latter supports as of now is MongoDB.
If some of the contributors to those projects were interested to help Jakarta NoSQL they would be able to benefit just like they and many others do from Servlet or other mature Jakarta EE specs. If they don't, then maybe it won't leave the incubator. JSRs were also withdrawn or went dormant for various reasons.
I'm not in the PMC, but other than that I wear multiple hats regarding Jakarta EE and NoSQL, so I know several aspects of this discussion and decision making.
Werner