How about setting it up a bit different then... with user accounts. Ex. you can deposit/withdraw a minimum amount, and then that goes into your inventory. As it's transferred from one person to another it would just stay in the game... kind of like Just-Dice (deposit on to their site, then you're no longer bloating the blockchain since you only add on to it when you deposit more or withdraw your winnings).
There are plenty of secure ways to ensure that player balances are kept properly... MMO's have been doing it for many years, :p. The main way they do it is by having a database that gives each item a uID.
Ex. there are four of the same longsword out there. While they are all named "longsword" and have the same stats, their uID (unique ID's) are 1, 2, 3, 4, so none of them could ever be cloned since there can only be one of each. As another is added to the game (drop or whatever) it gets the uID of 5.
I am very, very interested, if you guys are serious about pursuing this, in helping with game design documents and such. I think if it's done right it could be BIG.
Most free open source games do not maintain fully relational databases. heck even most supermarkets do not.
Rather, things get 'stacked' and abstracted.
The supermarket might know how many cans of beans are in each warehouse, but typically does not know - not maybe even particularly care - which can is in which warehouse. You could sneakily exchange any pair of cans of beans because any distinct ones that are known to be different, such as damaged cans of beans, would be a separate inventory item but again no fully relational. Most engines for fully relational databases died off because full relationalness was mostly of theoretical interest for relational calculus not often of practical use in the field.
So hey who knows maybe if you bought a copy of EVE online or World of Warcraft server source code you would find there is no such thing as ten swords, because ten swords is not a thing, there are ten things, each is a sword, and each has different fingerprints and scents and history so that a psychic could tell which of them once was used by so and so, which is stolen and from who, which one sold where to who from who when and so on.
But in free open source games I have not seen such accounting/inventory yet.
Oh wait, maybe a MUD comes close, if it does not implement stacking/bundling.
But once you stack or bundle there is typically no going back to which item in the stack was which individual item before the stacking or bundling; it is partly a way of saving data space by reducing many database rows all saying sword to one database row saying fifty swords, type of idea.
You could illustrate it in OpenSim by rezzing fifty models of swords, each with their own object-ID, or by rezzing one model depicting a bundle of swords and maybe using less than fifty prims.
-MarkM-