Apparently, Sean O'Keefe is considering using Soyuz as the ISS crew ferry vehicle, even after RTF.

The article points out that NASA may end up having to buy seats from the Russians, but I hardly see that as a crippling expense. If you take the going rate for a Soyuz flight as $20M/person, and assume that the three-man crew is fully-rotating (that is, no taxi pilot), and that current crew composition rules apply, that means paying the Russians at most $40M for a crew rotation. How much would it cost to send those same two astronauts up on a Shuttle...particularly if it means sending a Shuttle up on a rotation-only flight that might otherwise be eliminated? Granted, the cost of additional Progress flights would have to be added in, since the rotation-only flight would probably carry an MPLM along for resupply -- eliminating that means moving those supplies to multiple Progress flights. But it's hard to see it needing to cost any more than Shuttle, overall.

Also mentioned is the possibility of keeping two Soyuz docked to ISS, as a means of achieving the six-person crew target. How shockingly obvious.