Is it so complicated!
The name "BitUSD" is like a brandname - it is instantly meaningful as a crypto with a stable pegged value. I think its important not to dilute that.
Also, I have been thinking about what Dan said about launching new chain versions. He said that when a new Bitshares X version's chain is launched, all share holders will be copied over into the genesis block of the new chain, but all BitAssets will not. That means there would be a race to sell your assets for shares, leading to the peg probably breaking down.