Discussed in AV-42129 – Capella would like an XDCR source/target connection pre-check feature for XDCR out of Capella instances to self-managed clusters.  A feature like this would be best to do in the Server, and it would also be useful for all customers (since all customers have to deal with networking, firewalls, etc).  

So, a connection pre-check  1) as an option that can be done when a remote is added and 2) as something that's done automatically when starting the replication.

Side note:   mentioned that Support (See duplicate ) has been wanting a feature like this as well since 2016, as XDCR source/target connection issues are not uncommon.

 
NH: 7.2.1 is probably a good vehicle needed for Capella intergration work.