Good idea, but counter to bitcoin principles
No it isn't, its a voluntary market which other exchanges can participate in to improve their liquidity and competitiveness.
It promotes decentralisation by making new, competing exchanges viable without having to have large customer bases
and you would have to force exchanges to partcipate.
No you wouldn't, exchanges would be free to participate or not.
Also there is no real lack of liquidity. It's a lack of pricing stability.
Try selling >1000 bitcoins on any market other than MtGox without crashing the price 10%.
Price stability is a separate issue.