The intention of this project is great. But I doubt if it can even work well. The whole project depends on the fact that everything to synchronize can be standardized. But this is almost impossible.

Let's say "Birth of Date". Some contact providers support BOD without year. But some support only the whole date. If the companies do no even agree on this tiny little item, how can they agree on larger deviations? Like max number of phone numbers in a contact profile? The size/format of profile image? Address format? and so on