So Pyke and Urgot get indicators when their target is close in execute range. Why doesn't Darius?
Darius ult can be stopped by shields, but so can Chogaths and he gets an indicator. Darius ult resets, but so does Pykes.
It would just make playing him so much smoother imo.
It does
It's called quick math
Execute's are based on maximum HP, Darius doesn't have any execute mechanic because none of his abilities are based on maximum HP (par Q healing) or minimum HP, it just has a threshold where it'll kill - by the same deliberation, Orianna's Q would be an execute because her Q would be killing them.
Executes are defined by having an ability based on an enemy's HP like Pyke R, Urgot R, Pantheon Q etc
the execute indicator would be constantly changing for him, it just wouldnt fit him i dont think
Darius players dont need an even bigger handicap against the majority of top laners.
Braindead champs don't need to be made even more braindead.
Riot generally doesn't love too much indicators (as they add visual clutter).
While this is arguable reasoning, they follow two general rules:
has indicator because he gets HP for executes.
has indicator because of his gold share
has indicator because the execution also CCs
gets no indicator because in the end the only thing his reset does is dealing more damage. One can say it's controversial considering it's a crapton of damage and because he has tiny effects attached to ult cast (lunge + minion fear) but since he has another indicator already in his kit he most likely won't be getting execution indicator.
Notice that this applies not only to execute indicators, i.e. 
and 
get per-target CD indicator, but 
and 
don't.
