That makes an awful lot of assumptions about a lot of things, for instance that the huge costs in developing even "mid range" performance hardware with an exotic PPC such as the one in the PA6T for starters. It assumes also that the X1000/460 ever sells enough to recoup those costs or that PPCs that are in any way useful to the desktop are still available, consider that the PA6T being used now is basically warehouse stock that will never be replaced.
Rogue on aw.net has stated that they have already choosen a CPU (or a CPU family) which will be used in the X1000's successor, if this option would not have been available they probably wouldn't have chosen to support the X1000 project. The 460 has been made thanks to the good enough sales of the 440 (as mentioned by m3x), at least this is an indicator that there are possibilities that the 460 will sell enough, too.
Varthall
