So is the 2x BTSX that you need to borrow bitUSD based on the USD price of BTSX or the units?

If BTSX is trading at $.50 each, then I need 4 BTSX to borrow 1 bitUSD?

So, the whole bitshares concept could have been done on the NXT blockchain using NXT as the store of value and creating a bitUSD asset. (I assume they didn't cause the devs could create BTSX's for free.)

I wonder too, how close this is to the NXT monetary system. It sounds very similar to me.