We've already seen this plan in action--it was called Team Roberts 2007.
Engine leasing will fail mainly b/c the teams don't have the funding or the technical expertise to develop the obnoxiously sophisticated electronics required to extract maximum performance from only 21L of fuel. Until the governing body rev-limits and then raises fuel back to 24L, the sport will continue to get more expensive and feature fewer bikes.
If they don't raise displacement after 2011 and figure out a way to bring more engine manufacturers and more variety into the sport, I'm done.