I agree that clients prefer/want their consultants onsite and many of the companies won't compromise on this. But for the ones where cost is the primary factor,

I agree that clients prefer/want their consultants onsite and many of the companies won't compromise on this. But for the ones where cost is the primary factor, they would just keep the critical people onsite. (Onsite coordinator, architect guy etc.,). Regarding timezone, consulting firms already run several projects matching US time. The whole thing is so complex and has so many facets that there is no straight forward solution to it.