I really do think that allowing multiple slots to cause epic synnergies could be awesome (and having multiple of the same item to level it up would also be epic
I am currently working on passives for the next update :D Health upgrades and passives will appear in the shop. I would also love to be able to combine weapon parts, but that would take a lot of time, so it wouldn't be added soon.
Thanks so much, though, for the support and feedback!