Good idea, @Robo4900 !
Funny, my teammate's opinion is the same as yours.

My opinion is that the variable detonation timers should be the default, and the powerup could make the weapon even more useful.
The proximity idea is kinda boring, the charge already blows up if an enemy touches it, so it should be something more... awesome.

Like it could become physically active, or it could be thrown/launched, then stuck to the environment like a sticky bomb.