A purported replacement to the EF 50 f/1.4 was mentioned today in the form of an EF 50 f/1.8 IS. The lens would be smaller than the current 50 f/1.4. There is no imminent announcement of such a lens, but Canon is working to replace the 50 f/1.4 sometime in the next year. The current 50 f/1.8 would remain in the lineup.
Sounds plausible to me.