My recollection is that back in 2001 GM was developing the Zeta platform on which the Velite was based. I am not sure about the Bengal, but the history of the Zeta is that GM had two competing platforms in development and they chose to develop their pickups, which finally were introduced in the last two years, and abandon the Zeta.
Holden, GM's car company in Australia, decided on their own to develop the Zeta. This was pure luck because the pickups were introduced right as the heavy SUV's and pickups were suffering slow sales from high gas prices. GM looked to Austria and borrowed the Zeta on which to base the upcoming Camaro, which comes to market late 2008 as a 2009, and the Pontiac G8, which will go on sale soon. Apparently, 1500 are on a boat somewhere coming to the US as I write this.
Kappa was introduced as a concept platform in 2004. It was intended to be a flexible platform capable of being stretched from a 2 passenger to a 4 passenger car. In development, certain compromises where made to bring the Soltice to market on time that now prevents GM from introducing a 4 passenger version. It can't be stretched as originally planned. I saw the concept Soltice, and the four passenger Chevy Nomad at the 2004 New York Auto Show, and I preferred the Nomad.
In two or three years, GM will bring out the Alpha platform, and a new small 4 passenger Chevy and a new Cadillac will be introduced that will compete with the 3 series BMW. Again, all of this is courtesy of Holden. The Aussies have a real appreciation for RWD. The next Soltice and Sky will be based on the Alpha platform. Apparently, it can be shortened for 2 passenger sport cars. GM promised to include aspects of the Kappa platform in the new Alpha platform. When Soltice and Sky move to Bowling Green Kentucky it will be as Alpha platform based cars. I believe the timing is somewhere around 2012 or 2013.
I read a lot of general auto blogs daily. This is what I have picked up so far.