Being able to take an item out of one game and move it into another game sounds like fun but keeping track of the ownership is a tiny problem compared to having the appropriate assets to draw the objects cross-game never mind implement the attributes of the objects. (And not let imported object "break the game")

If you had it all in a unitary system like the OASIS from Ready Player One it might be possible but unless all the games are under the same framework it would take a lot of coordination.

In the hope that it'll be worth real money someday, and you'll get rich off of it. That was even in Neal Stephenson's original concept of the metaverse. And it's what explains very nearly all of the money in today's virtual currency markets.