Whilst I do think some more ways of getting inventory weight through ingame methods is a good idea, and I do have some ideas for how to implement this with some future content, I'm not sure if the methods you've outlined here are the best way forward for this.

Better methods would probably involve using cash alongside other resources and a set amount of time to boost inventory weight by a set amount each time, with increasing difficulty for each increment, but in such a way that it's integrated into gameplay in some manner, and that is possible for all players to achieve given enough playtime / grinding.