i cannot understand why canon should produce an entry level FF. They have one it's called 5DmkII and apart from autofocus, 2.1 fps more and about 2/3 stops improvement in high iso - please don't mention 2 stops I am referring to raw files- it's extremely close in IQ to 5DmkIII.
Canon can replace the metal body with polycarbonate, and the penta-prism with a penta-mirror. In short, introduce a FF sensor into a small and lightweight body (600D). Market that for ~US$1500 and it'll sell like hot-cakes.
I'll like to see Canon limit DSLR bodies to FF and convert all APS-C cameras into compact camera systems. Perhaps that's what Canon has in mind and that's why we're not seeing the usual yearly replacement for the 600D.
That's just my preference.