If you want to look at free to play economies, the most successful, largest player base and money laundering game is still TF2.
Which has duplicates out the ears and down to the pub.
And, oh boy, this is the kicker. You know how much rage the community inexplicably has for getting duplicates rather than 'good things'?
Imagine if you also got crates dropping. Which you had to pay to open... and still had a chance of getting something worthless ;D
Except in tf2 duplicates are actually wroth soemthing becayse of crafting and trading.
We should applaud Relic for removing the ability to pay for commanders but duplicates have no use right now. So why have them.