What change do you want to see on your main class for Endwalker ?

[Raikai]

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.

Wildfire... yeah, would remain Wildfire in the end of the day. I think a redesign is overdue on that. I hated the SB ping aspect of the ability, but the functionality: as in benefiting from your good hits to be more powerful in the end was better than just the number of weaponskills shoved into the timer like it is now. If they had the previous Wildfire iteration but without the whole ping downside? Maybe making it work like NIN's Bunshin?

Overheat works... but it's so bland to press the same button 5-6 times, even visually, your character just loops in the same animation. I can totally see something like changing the 1-2-3 combo into unique weaponskills with effects that interact with each other in a non-linear way. Or at very least add something else to combo with Heat Blast during Overheat so we don't just see the same thing over and over again.

I love your ideas with Reassemble, they could give a nice punch to the machinery without adding more buttons to the job, and they don't even need to rework the ability in itself, they can just give a trait between 81-90 to augment it.

Just a QoL, I wish that Spread Shot, Bio Blaster and Auto-crossbow didn't require a target to use.