If someone believes the LTC/BTC exchange rate will increase then they would take that loan.
No, what im saying is that if you already have the amount of money you need in altcoins what would be the point of asking for a loan
The only scenario such collateral makes sense is what DAT said.
Imagine you have 100 LTC and you're absolutely sure that LTC price (expressed in bitcoins) will go up, so obviously you want to buy more of them. Selling 100 LTC to buy 100 LTC doesn't make any sense. So it's best to borrow bitcoins (using LTC as collateral), buy more litecoins. When (if) the price goes up, sell LTC, repay the debt and enjoy the profit (+ sell those 100 LTC you got back if you want to).
Simple.
Wait, what you are saying is that someone wants a loan of btc to buy ltc giving his already owned ltc because he believes ltc price will go up? Seems pretty stupid to me