Sorry, bit BitShares has had this for 2 years!
BitUSD, BitGOLD, BitBTC, etc.
1. They have 20-30 market pegged assets. Market pegged assets over Bitshares have nothing to do with the leveraged trading over MaskNetwork. We are talking about different things. Check market pegged assets section in MaskNetwork.
2. Because the price feed has to be implemented by over 50 delegates, the whole Bitshares system is inflexible. Implementing a new asset over Bitshares right now is really difficult. Over MaskNetwork a new currency market can be added in minutes if there is a data feed. Data feed providers have all the interest to offer as much assets as they can because they get a fee when a market uses them.
If a data feed is providing the outside weather temperature and someone starts a market then you can trade it.
Sorry, you will not see Monero, Ripple or any other smaller cryptocoin over Bitshares anytime soon. But it's trivial to start something like this
http://maskwallet.com/pages/assets/margin_mkts/market.php?ID=8693914066 over Masknetwork.