Apologies for the late reply! Thank you for playing our game, glad that you liked it <3
Hold-down button is a hot request and we plan to add it if the current shooting rate remains (that depends on where we will land after enemies refactor).
New weapon or weapon mode is surely on the menu. We are currently discussing in what form we will introduce it and what new mechanics it will bring (like overheat for the TimeGlock).
We are currently expanding the game with features that we planned for the jam but didn't squeeze in, like mini-puzzles to solve from time to time, more robust enemies, more fleshed out story, proper animations, cutscenes, more diverse environment etc. It's gonna take some time, but we are determined to finish it and learn more from it ^_^