Desi is bit of a strange term for some. As a person of Sri Lankan origin, I don't know any other Sri Lankans who refer to themselves as desi. I didn't hear the term myself until college. I don't know why we need a new term when "South Asian" is perfectly adequate.
South Asia is pretty colorful (at least compared to Han-dominated East Asia). I do think they have "South Asian" as an option on many query forms now.