That kind of inconsistency in the control scheme isn't acceptable from a design standpoint, and the F-keys already have their own uses.
As do the number keys (show enemies, items, etc). Only with shift/ctrl/alt they are used to manage the inventory. The F keys could be handled in the same way.
Technically not every keyboard is guaranteed to have F-keys, or they're not always easily accessible
Granted - but with that argument, no roguelike would support numpads.
If I were to add this feature the only partial solution I see is to make an extended inventory only available to mouse users, though that "solution" then goes against the principle of making sure every feature is accessible regardless whether using keyboard or mouse.
Agreed, any feature should be available to both mouse and keyboard users.
As an alternative approach, remember that you can use t/m/i to forward-sort and reverse-sort your inventory based on different characteristics, making it possible to manage even large inventories fairly easily with the 10 slots that are available.
I know the sorting features, but they do not solve the problem that you cannot see all your inventory items at once.
The main reason why I love Cogmind's interface so much is because you can see *everything* on the screen - equipment, inventory, etc (not like in other roguelikes like nethack where you have to scroll through multiple screens of items to get your stuff managed).
The only limitation to this is the inventory when carrying more than 10 items :/
If you don't like the suggestion with the F keys, maybe there is another solution?