Just like with pokemon. Say you wanted to loan an exp share to somebody for an hour, when timer is up you take it back.

It's hard as there are some single use items like lucky eggs, Stones and books.
So no point in loaning xD

I've seen this suggestion in the past. But it isn't implemented.

Eb makes a good point, but maybe if those one use items couldnt be loaned, its a good idea. I know people will appreciate this when getting a toxic tm for halloween hahah

I don't think there's any special need for items, since there are very few items that actually have unlimited use(like farming gloves or dowsing machines). It isn't completely pointless, but it has far less use than other things.

I completely agree with the others. It'll make items such as; Books, Lucky Eggs and other Consumables useless.