I've started to play some Brimstone recently, mostly because of how strong his molly his, besides his smokes are easy and fast to place, however, his stim beacon is an ability I rarely find myself using and when I do I don't really feel a difference. I think with some simple changes he could be way more viable without making him overpowered:

-Make it give a faster reload time, I think 25% could be very strong.
-Slightly increased radius.
-Reduction in the duration of the effect when out of the sim beacon to 4s.

So, basically just a faster reload time.