Will US Policy be that there should be two Boeing CST-100 Starliner or SpaceX Dragon V2 craft attached to ISS at all times for the American segment of the station? Will Soyuz continue to be used?
The current plan is that the Russians will maintain a Soyuz vehicle at the station at all times there is crew aboard, allowing for 3 crew members.
US Commercial Crew (Boeing CST-100 Starliner, or SpaceX Dragon V2/Crew) will be maintained on the station at all times there is a crew aboard, allowing for 4 crew members.
Currently with 2 Soyuz the maximum (Though of course, there are 4 Russian docking ports, so potentially 4 Soyuz, but usually 2 Soyuz, a Progress or two, and possibly an ESA ATV is the compliment of vehicles) there is a maximum crew size of 6.
By moving to 7, (3 on Soyuz, 4 on Commercial Crew) they gain one more member, and since after maintenance, exercise, and other administrivia on station, the entire crew of six, only manage to accomplish about 40 hours of science experiments a week total. Thus adding one more person, should add 40 more hours a week of available work time, which could double the science throughput. (Assuming that their time is not consumed in incremental tasks based on 6 vs 7 in the crew).
Thus no one is getting kicked out until the Russians decide to leave the station.