The "Pegasos2.5" is only a nickname for one of the Freescale reference boards with the Genesi Open Firmware. Nothing more.

There is no product from Genesi announced (or even rumoured) that will use the Marvell Discovery V. At least not yet.

The server blades uses the Tundra TSI108 (at least AFAIK), and is awaiting the arrival of production level 7448's in volume (again AFAIK).

The next product similar to the Pegasos (full motherboard aimed for workstation/server usage) will be a dual 970MP (a dual-core G5) motherboard, something like this. It will be MicroATX like the Pegasos1/2 but it will have the CPU's mounted horizontally instead of vertical like the current Pegs. This will make it possible to use thin cases, like a 1U server rack for instance.