If Flare was thinking of Boosting another tower, then I think FireBolt would be the best option.
I have made this suggestion a long time ago but it seems like now it is more likely to be heard.
A good way to boost FireBolt towers without making them a copy of another boost would be the “DualBolt Tower”. When boosted the FireBolt would shoot 2 bolts instead of 1. Each bolt would have the damage of 75% of the normal Firebolt. But each boost needs something that can increase with each level but wont be OP when max. So instead of increasing the strength each level could increase the amount of time the fire damage lasts.
It would be hard to integrate a new boost into the game, but maybe Flare can put this idea in there pocket for later.
What do you think about the mechanics and whether or not we need more boosts? Personally I think this should replace the useless Arrow tower boost.