It will also be a great idea to add custom comments section for existing objects on a map. For example, to define what frequency is in use at an aerodrome at a particular time or direction of flight (because in SD there are duplicate frequencies like RADAR 1, RADAR 2, without further explanations compared to AIP, like you should contact at least 20NM out), describing a navaid functionality (min/max working altitude) or just whatever you deem appropriate to include.

I think it's not overly complicated to implement this, but it adds a lot of flexibility to have your own notes without creating additional objects on a map and make it more messy.

Another good thing in addition to that would be a gps-location based reminder (w/ altitude). Just like the current airspace warnings, but it would show your message instead.