So I was trying to think of some QOL things that wouldn't change any of the skills of MCH that could make it appealing to more players that would be somewhat on par with AST changes throughout heavensward. I think QOL alone would help machinist a lot similar to AST.

1) Make the bullet UI glow red while Hot Shot buff is up. Let the circle UI for heatgage only glow red when overheated. This is nearly more important to track than bullets.
2) All your basic "shots" to upgrade automatically when triggered, reducing the number of buttons needed (we have like a million off-gcds, I have more button bloat on machinest now than I did before). This would make that element similar to that of pvp machinist as far as UI goes (but still follows pve rules for upgrade...aka not 100%).
3) Make Gauss Barrel Reapply after overheated cooldown. (again, one less button)
4) Turn the crit ability to apply all currently loaded bullets. This means up to the next three bullet consumers will crit.
5) Make the turret's follow you like a carby. ST turret shoots from range, and AOE turret gets into melee. This way they'll move with mob packs when the tank is dodging mechs and stuff.

Anyway, those are just my ideas.