>>I will report back any issues as I test.
So far, no major issues. I've set up a supplier replica from our CentOS 7 service running 1.3.10 from EPEL 7 and all seems well. It did require a tweak to some legacy schema files that are still hanging round from when we used the "Sun Directory Server" way back in the day, that has been the case ever since we moved from the Sun DS server and upgraded to 389. At some point I'll clean up and remove the old data from the directory that references them.
I also had a small issue setting the SSL cert via cockpit, where it would keep reverting to the self-signed "Server-Cert" . On reflection, it could have been because I was trying to use an expired cert, rather than the current one, but it didn't say there was a problem. I set it manually via dse.ldif in the end.