In-game server latency:
Players should be able to see their (and ideally other players) latency to the server. This should be displayed on the scoreboard. Additionally, displaying the connected server (EU Central, NA East etc) in the detailed performance stats could be helpful.

Mouse sensitivity to real-world units:
I hope this becomes a new standard for shooters. When setting a mouse sensitivity in the input settings, ideally there will be some information on the cm/360 or inches/360 for various DPI settings. This will greatly help players translate and refine their sensitivity when coming from another game. Battlefield 6 does this and it's incredibly helpful.