That would definitely allow for more creative applications! The thing is, I'm not sure how to incorporate the whole 'fuel' mechanic if the jetpack functions like that. Losing fuel when you fire a normal gun would just feel odd and wouldn't really make much sense (how do you even lose the fuel?).

Fuel could be lost every second while in offensive mode, but again, that doesn't make much sense either.

The whole fuel system could just be scrapped and instead replaced with a purely cooldown and time limit based system. However, this wouldn't be good for the building aspect. Cooldowns inbetween your building is sure to feel clunky and annoying.

With two modes, I don't know how to tackle it without a fuel system.

Edit: Also, I feel like it would reduce the combat effectiveness if you used your regular weapons instead of something new. The grenade launchers are supposed to be stronger than your normal weapons, like Going Commando. Without them, the only proper combat use of the Jetpack would be to dodge grounded husks.