Obviously he has a vested interest, and I think Carmack has been pretty loose in his next-gen console observations. For example if he really thinks X1 and PS4 are 'essentially the same', it might explain why he thinks the above...
That aside I think he's being quite conservative indeed in that. A 720p/60hz game on PS3 will translate to better than 1080p/3d/60hz/MSAA on PS4 unless you're doing a very naive straight port. And it ignores the multitude of software/technique improvements that emerge between generations.
I think it'll be interesting to hear how EvE Valkyrie is on Morpheus - one of the better looking Rift games to date, IMO.