Grizzly is no longer being actively developed. Recent problems with JDK11/TLSv1.3 indicate that we should consider migrating from Grizzly, ideally before 7.0 is released since that is when we want to have a stable SDK.
This issue can be closed once we have replaced opendj-grizzly with a home-grown NIO based transport. We should look at what we had in the 2.6 server for inspiration. We have considered Netty but decided against it since it is a heavily used and heavyweight library that would significantly reduce the usefulness of the LDAP SDK.
JNDI also has an interesting threading model which makes it very easy to develop high performance client applications that are safe from deadlock in situations where applications reuse the same connection for performing bulk operations across search results. However, it's single thread per connection doesn't scale well (imagine AM with 20 connections per pool and 3000 realms).