Not in WC3, the 6 item limit is hard coded. This was something improved upon for SC2 where you can fully customize the number of inventory slots.Is there any way i can increase the inventory size to like 8 or 10?
Care to elaborate how to add items to a hidden spellbook? Note I am not referring to the abilities on the items, but as you said the item widgets themselves.The default one can be increased by a hidden spellbook, but the excess items go to the hidden spellbook's inventory and are thus invisible. So it's not advised.
The reason why not many maps use it is because inventory swapping is a mechanic that is not intuitive for the end-user. Sticking to the default inventory and just adding a second unit following you around that holds six more items is easier to understand for any new player and usually also better managable.Never knew about that. Surprised more maps have not used it.