There is already a non-persistent hide UI feature. From the readme:
• Hide/restore the HUD from the main menu using the 'F3'/'F4' keys, respectively. Scar will be impervious to damage and fatigue while the HUD is hidden, yielding a sort of 'god mode'.
Not sure about adding a persistent one... the game isn't really meant to be played that way. Any indicators would be gone, too, so you wouldn't know if you're bleeding out or dying from radiation sickness, for example. That's because the CS engine doesn't recognize the hud_draw cvar in gold master mode, so any toggle would likely need to be implemented via the hide_indicators/hide_indicators_safe Lua functions, which hide more than you'd probably like for normal gameplay.
The reason why the existing, non-persistent toggle works is that it also enables god mode, so it doesn't matter if Scar is irradiated or about to eat an enemy grenade - he's impervious to damage anyway while the UI is hidden. Obviously, this mode is not intended for regular gameplay, just for the occasional Zone tourism (e.g. screenshots).
Decane1
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