Instead of having to have hotkeys, why not have buttons on the inventory GUI that do the sorting?

Similar to how inventory tweaks is for minecraft? Also buttons on the chest gui. That would be awesome

I could try, but it's probably going to be very hard or even impossible.
The reason is: There's no way to know where the inventory GUI is and what properties it currently has (none that I know of anyway).
I could do something like the buttons appearing on the right side of your HUD when you open the inventory. Let me know if you want that or not, it shouldn't be too hard to make :D

Ah right, did not think about that. Well it's up to you if wanna add that :)

I think I could make it optional in the settings. That way you can use it if you like or just ignore it if you don't.

This has now been implemented in 1.4.
Unfortunately I didn't realize that it's not possible to put the GUI on the right as I'd like to, so it's on the left now. It might be a little confusing if you have a lot of mods that add GUI there though.