Wait? You didn't like automatically sacrificing an animation-lock's worth of Overheated's 8s duration, dropping it from max 6 (8/1.5) shots to max 5 (slightly under 7.5/1.5)?!

Personally, I'd slightly prefer a different tack, if only because I dislike button-bloat:
  • Hypercharge Overheats your next 6 shots; 12s max duration.
  • Heat Blast, once acquired, replaces Hypercharge while Overheated.
  • Auto Crossbow, once acquired, replaces Spread Shot / Scattergun while Overheated.