I never understood how would anyone use an altcoin for collateral, i mean if you want 1 btc loan but you have like 100 ltc, why not sell the ltc yourself instead of asking for the loan?
Some people like to keep the coin. That's like saying if you're using your house as collateral, why not just sell it and buy bitcoins with it.
You cant compare your house to some altcoins. First of all selling altcoins is the easiest thing and also fast, selling your house is not. For me collateral should be something that you can sell somewhat fast and safe but altcoins as a collateral is like having 70k dollars and asking for a 50k euro loan using 70k dollars as a collateral, makes no sense.