[T]he whole idea behind BTS X is to establish price ratios without having an external price feed using just a prediction-market-like mechanism.
Backed assets issued with BitShares Me probably will be a bit easier for people to visualize. They will be essentially warehouse receipts.
BitAssets most likely will be issued to track the 'usual suspect' assets first, including USD, EUR, XAU, XAG, CNY, JPY, etc. Once people are used to those, it will be fun to see how the market prices BitUnobtainium, BitVaporware, and BitNothing.