Russia to develop and field MiG-31 Foxhound replacement by 2020

"We have started development of a new aircraft of this type and I think we can develop this plane before the state armament program ends in 2020," says Lt Gen Viktor Bondarev, commander of the Russian Air Force. "The new plane should replace the existing fleet by 2028,"

http://www.flightglobal.com/blogs/the-dewline/2013/04/russia-to-develop-and-field-mi.html