Interesting thought...but I think this is just a pipedream.
Apart from the extra R&D costs involved (for an 'entry level' product that, as such, would probably sell at lower profit margins), production facilities are still recovering from events earlier this year.
Refresh cycles have been delayed across the board as it is-I doubt whether there would be enough headroom for an extra level in the range.
If they really would want to do something like this, it would be far simpler to lower prices on the 5DII, keeping it current alongside a new, and much more expensive 5DIII. But they can't make enough 5DII's as it is...I don't see that happening either. And you certainly can't just stick an FF sensor into an existing APS-C design, the metrics and dynamics are very different.
Actually, FF cameras aren't entry-level product by definition-they do require bigger and better glass too, and longer tele's to make up for the lack of crop factor...and, just in case you hadn't noticed (ouch!), quality glass is getting more expensive by the minute...