Great idea, but I shouldn't be adding new weapons.
Maybe I'll add them in the next game. ヾ(•ω•`)o
You could put it in the next game but if you make new weapon on the same engine and art style it is equal to less time wasted in the future and the only thing you really would need to is make locations and enemy type. Also if you were to be a bubble of text that could have Easter egg to one of your other games you have created.
Good idea or a I will think about it?