The Guardian has some detail on a time line for Project Kangaroo that may see it launch in March 2009. To meet this deadline it is expected that a closed trial would start in January 2009.
Project Kangaroo is set to take over with providing video on demand content for ITV, BBC and Channel 4 once it has dropped off of their free catch-up services. The catch-up services have proved popular due to being free and the ability to watch shows that you forgot to otherwise record, or was lost due to a PVR crashing.
How popular a paid for service will be remains to be shown, it has competition in the form of DVD box-sets and the various DVD/Blu-Ray rental services.