Thanks for those links Donnchadh.

Let's split the discussion into 2 parts:
1) provide a hibernate-hikari module to integrate HikariCP into Hibernate as a standard ConnectionProvider implementation
2) make hibernate-hikari the default ConnectionProvider implementation

(#2 depends on #1).

Should support for HikariCP be provided as a standard Hibernate ConnectionProvider implementation? To me the performance characteristics are secondary to answering this question. The main considerations should be:
a) how popular is HikariCP with the Hibernate user community?
b) is HikariCP a correct connection pool implementation?

If lots of Hibernate users are using HikariCP as their ConnectionProvider and if HikariCP is (not more so than normal) bug-free, then it makes a lot of sense to considering integrating it into Hibernate ORM.

The second question is all about performance and the commitment of the developer/maintainer to keep up with it, imho. To me, it sounds like the performance aspect is quite undefined.