I would love to see 2 features that might be mostly photography-related.
1) distance rings
It's important for me to know the scale of the map and even better to see distance rings to know how far away e.g. particular clouds are from my chosen standing point.
2) sun position
To see where and when the sun rises or goes below the horizon as well as the position of the time shown on the map would also be very helpful. This could be used to determine afterglow in the morning and evening. For afterglow clouds are lit by the sun from below. To determine times when afterglow could happen you need to check cloud coverage in the area above you and the areas surrounding. If there are no clouds blocking the light from the dawning sun reaching those clouds above you, you will see afterglow like this:
I've created a mockup in Photoshop on how this could be displayed in Flowx.