Tier 1: When pressing E on a placed C4, it is automatically activated by a pre-set, adjustable time.
Tier 2: C4s are automatically activated when placed or dropped.
Tier 3: C4s can be activated in a separate panel, similar to radios.
Thanks to @iii we know that C4s can be triggered by commands, and while we don't allow this or similar scripts to be used on the servers due to potential for unfair play, by creating a defined and accessible way for this ability to be used it would negate the disparity between the average player and the technically inclined.
Pros:
> Faster C4 placement, more time playing.
> Would allow for more impressive and strategic explosions.
> Drive-by C4s, similar to placing a Deathstation except without the possibility it's harmless.
Cons:
> Clue.. and other small maps where a synchronised C4 explosion could functionally create dead zones within 60seconds < C4 capping would need to be implemented to negate this issue.
> Could be just as fiddly having to open a menu each time you wanted to plant differently timed C4s in short succession < Could implement a Keybind to de/activate the Perk similar to disguiser + you can walk and use menus.
> Without radius limits C4s could be activated cross-map leading to Common-Sense rules issues < Radius limits to T3 activation &/or Line of Sight (I don't know the feasibility of this).
The mains issues arise from remote activation, but not unsurpassably, so if you've got suggestions on ensuring fairness while including it please share. Otherwise, quick planting C4s is easy enough with practice, now you could just buy a perk and never worry about it again.