Wildfire
I wouldn't do that for multiple reasons:
-Queen takes 3 seconds to boot, nothing hard but you'd have to use it 2 GCDs before the actual wildfire.
-You'd lose the Flexibility and makes the battery gauge always used at the same time.
-Wildfire would remain Wildfire, AKA apply and forget.
If Wildfire was heavily reworked, why not. But with the current version, you could simply remove Wildfire and MCH would even be better.
Overheat
Anything is better, yes. You could even make all 123 shining so you'd do a 3-2-3-1-2-3 at 1.5s GCD and it would already be funnier than spamming the same button.
Reassemble
I thought aswell of giving reassemble different effect depending on the machinery used. And I think it's a good idea but how to do it well?
Refund cooldowns, allowing to freely use a Machinery action without putting the ability on cooldown? Things like that, that could be a nightmare to design.
But I think "A button with multiple functions" is a good idea for Reassemble. Drill a guaranteed Crit/DH, turn Air Anchor into an AoE, Bio Blaster a stronger/longer dot...
I think there's a good room to implement the multi-function idea and adding more AoEs without dedicating a whole new button with a shared cooldown on it.