Actually, a friend just went through this. A long time user of Glassfish/Payara and EclipseLink. But he wanted to do some specific things with multi-tenancy that had better support in Hibernate for the way he wanted to do it. EclipseLink has multi-tenant extensions as well, but didn't support exactly what he wanted to do. So he switched. He didn't have to toss out his platform implementation (Payara Microprofile I believe) just the JPA implementation it was using.

All of his other JPA stuff ported over, the multi-tenancy is on the edge of it. The whole point is most of his code is ignorant of the multi-tenant aspect. But, also, the JPA spec itself is silent on multi-tenancy, so it's no surprise that the implementors are trying their own approaches. I have to assume that whenever the next JPA spec comes out, it will take inspiration from all of these different implementations and come up with a mechanism to standardize support for them.

So, while he's now "locked in" to the Hibernate implementation of JPA, he didn't have to toss out JPA itself, or his platform. If/when JPA catches up, he may well be able to have the option to switch away from Hibernate if he chooses.