Update:
v0.12. Changes:
- added Backtracking feature: assign a key, hold it to reverse movement from short time period. Useful for unlucky falls and getting out of encounters that are too surprising.
- added Breadcrumbs feature: shows from where you came. Goes well with Backtracking.
- added red pulsing highlight for exit sectors (optional).
- made speedometer size and position configuration options. I still don't know the use cases for the speedometer
Regarding other features that seemed good some time ago:
- compass showing enemy positions: already implemented in Ultimate
DoomVisor HUD by saegiru, and maybe in other mods too.
- locations of keys, like in Guncaster: Guncaster does it by custom skills, therefore I cannot do it in the same way
and universally.
Edit: about "locations of keys, like in Guncaster": in new GZDoom version there will be a new CVar, am_showkeys_always, and setting it to true will do exactly this.