Building Blocks; At next week's East Asia Summit, there will be talk of creating a regional common market and, eventually, a single currency. Are those plausible ideas or a pipe dream?

Byline: Christian Caryl (With Joe Cochrane in Bangkok, Marites D. Vitug in Manila, Sonia Kolesnikov-Jessop in Singapore and Lorien Holland in Kuala Lumpur)

Just imagine: it's a sunny winter's day in 2045, and you're arriving in Bangkok airport on the 1:15 from Shanghai. The flight is considered internal, so there's no customs check; you can keep that dark red Asian Union passport in your pocket. No need to pick up any cash, either--you've still got plenty of yuen (the single Asian currency) left over from your previous stops, including Tokyo and Seoul. After your business meetings you head over to the magnificent glass-and-aluminum building that houses the Asian