We are not moving away from cultures as world wonders (WW) afaik, but I agree that WW's should not require a resource only provided by another WW.This looks like a return to vanilla in some ways. Is it really necessary to make these works rely on one culture? I have the feeling that this is totally against the spirit of C2C, which will become even more apparent when the present cultures are completely gone, as seems to be the (long-term) direction of the mod.
Another reason why this might not be a good idea is the fact that this system of great works can never be extended beyond our present era.
A WW could imo only be tied to cultures by reducing their cost if this or that culture resource is available.
The Xpunk cultures may be an exception though.