Wow, thanks for that detailed review! Nice analogy with the knapsack problem, I thought about it while developing the system, but forgot the actual name of it.
Your ideas for potential new mechanics are all interesting, those are all interesting ways to solve current design problems, as well as add different tasks for the player.
UX additions are also great!
1. I agree that current profit display on scales should be reworked: right now this information is placed in small font under the scales ("Salt buy/sale: 15/17, Current profit: +152" for example), but that's not really UX friendly.
2. I love the hotkeys idea, and I think it's the best way to implement them like that.
3. Regarding overlapping, I believe new version of Godot helps solve that problem a bit (at least now player will be able to pick up the front weight first), but for fixing overlaps, I might have an idea or two on how to resolve them~
Thanks a bunch for taking your time to play our game, and most importantly - to write this review to us, it means a lot!