1. Anyone with moderate coding skills can copy the SD model easily. It's simply a bot monitoring incoming transactions and creating raw transactions. It won't be surprising if there will be a price war, leading to a huge reduction in profit and increased risks
2. There will be a tx fee increase to deal with SD pollution SD (https://bitcointalksearch.org/topic/rfc-updating-dust-output-definition-and-default-fees-130450)
3. To buy S.DICE on MPEX you need to pay a ridiculous registration fee of 30BTC, let alone the cumbersome commands. Those "passthroughs" is the most risky part as you would never know whether the assets are really backed by real S.DICE.
Passthroughs are really multilevel of credit risk, ( in the whole chain, just one default cause you lose every claim you had).