I saw that there was a feature request for this on the forum too back in November of 2016, with the latest post being from April of 2019.

How come this is still not implemented yet? Especially given development on new games too.

There was also a feature request for this on other games like Factorio, where it was requested in 2016 and implemented in 2019 - the developer response for the implementation can be found here.

It should be a pretty basic thing to make, without taking priority and weight into account (not needed), having the game client do the following when connecting using a domain name:

1. Check if SRV record exists for domain - if it does, use the target in the SRV record to resolve the host.
2. If no SRV record exists, get A (or AAAA) record as usual.

SRV records are really useful for hosting multiple Arma servers from the same host, since players won't have to remember the port, but can instead just remember a subdomain.

It's also great for hosting the game on one server and a webpage on another server, and having both be accessible with the same domain. For example, say you have play.example.com - you could then have the A-record point to a webserver and then add a SRV record (with the same subdomain!) pointing to another A-record for the gameserver!

Hoping you will take some time to try and implement this into the engine/game :)