Personally, I like this.  Having played quite a bit of Heroes of Might and Magic, which doesn't allow this, I've found that arranging meetups for heros to swap items with each another can be a real pain. 

All the money, materials, etc your heroes find is instantly shared, why not items?

Yeah, I don't mind being able to transport items.  It feels unrealistic, granted, but it saves you from the silly micromanagement of sending your extra merchants or whatever gallivanting across the map just to get bracers from your eastern border to your western one.  This has always been a pain in the Heroes of Might and Magic series, as LintMan points out.

Maybe there's a middle ground?  After researching caravans, for example, maybe you can then send items across the map, taking X number of turns to get there based on distance.  Don't show a unit or a hero carrying the item, just transport it silently and in the background, as if you got some lowly peon messenger to do it, only without the micromanagement.  That way, there's not an unrealistic instantaneous transportation thing going on, but there's also not the same frustrating logistics problem.  You could even set the item to "auto-equip" once it reaches its target to further reduce micromanagement.

While this is true, I really don't know how having to move units to adjacent squares to give them stuff can "fun strategic decision making". You either move your giver to the receiver, receiver to the giver, or meet half way. That's about it for the "strategy" around item trading this way.

You could make it depend on the quality of the item, I suppose. Higher quality, higher cost.

I also don't like the super-swapping across the map.  Accessable from a friendly city "vault" or having the sender use some of his/her spell points would be good.  Troops can actually carry found equipment, they just cannot use them.

I'd say if in doubt, do it the MoM way.

of course the cost depends on the Mana System, 20 mana in MoM was maybe more (or less) than it will be Elemental?

although since this isn't MoM, I could live with the idea of a Caravan research or a spell to allow it.

It can be fun because it makes you look hard at a large map and weigh the 'time-value of asset transfer' vs. the value of keeping the asset-holder and intended-asset-recipient on other tasks. In the late game, transferring a simple enchanted bastard sword might not be worth re-routing any champions, but such a transfer in an early game could make a big difference in the long-term value of the receiving champion.

Also, making item teleports hard or impossible can add fun to a late game where a quest for a Very Important Item led the questing champion very far from your realm's centers of strength. If that's a truly major late-game quest and you know that getting the Item back into the hands of your sovereign or non-adventuring champion is necessary, then the quest itself is more interesting because you need to think about whether to send some support groups into the same general area where you expect to find the Item.

Hopefully a cost will be required to transfer across a distance, and that process will prevent a champion who's engaged in combat from then being able to transfer items -- both fighting and transferring would be actions, of which only 1 can be done per turn.