Having had time to think about this, i'm sceptical of the april launch!!!
Simply because, to go FTA C4 HD needs to move from it's current transponder on Astra 2A ( because of Astra 2A's pan-european beam and copyright issues) to a satellite with a 'UK only' focused spot-beam capability.
Currently only one of the four satellites at 28.2/28.5E has this capabilty, Astra 2D, and that has no spare capacity.
Astra SES will be launching a new satellite Astra1N (that will provide additional spot beam capacity @28.2E) however, as of yet there's been no confirmed launch date, just 'expected to launch in Q2 2011'.
So i'm currently wondering how they can launch on Freesat in april or where there the capacity has
miraculously appeared from...
EDIT - Looks like it's going to be shoehorned onto the BBC transponder