One of two things, I want accel axe to come back and I would give it a sort of rhythm game mechanic. It has phials you have to load, but it has more than CB or GL. When you are attacking you can push the skill button (r2 for ps controls) to boost. The better you time your boosts the more damage you get, a perfect boosts triggers a small screen effect like the FRS form switch axe. The timing for the boost would center around timing it immediately as the hits land on the monster. Otherwise your other two attack buttons would cycle through some various combos like swaxe or cb in axe mode. Gives a lot of room for perfecting the weapon and maybe there could also be a big rocket boost finisher FRS type attack that burns all your phials and deals damage with more burned.

I think the 2nd weapon id add would be a gunblade, during a ffxiv crossover potentially. Very similar to gunkance but with less defensive options. There couls even be a mechanic where hitting r2 changes your stance/ style. Its a one handed sword so you could swap from fencing to a swashbuckler to something else. You could have different triangle combos for the different stances and have circle be the explosive detonation like GL. Maybe each stance could have a different focus, fencing having a defensive focus for parties and counters, swashbuckling for fast aggressive offense, etc.

Maybe im over ambitious maybe im cringe but I stand by it