We are investigating if we want to include these modules. The fact that nvidia is no longer planning to maintain the 9631 driver doesn't help the case. We have to contend with possible bugs, mainly security related issues.
Not only that we have to contend with making the driver work with our kernel. If nVidia isn't keeping the driver up-to-date, we are having to modify the build ourselves to make it compile. We already had to do this with 9631. It will only mean more problems in the future as the kernel API changes. Additional work for maintenance.
For those that suggest this is a critical bug, it is not. A critical bug makes the system completely unusable (read the definition of severity levels on the Ubuntu wiki). Ubuntu's stock nv driver supports all of these chiosets. It boots and works as expected. The nvidia driver is supplied for those wanting the vendor supported drivers to get acceleration with their hw. We provide these as a courtesy, to make using Ubuntu easier for you, since we assume most people will want the drivers whether we provide them or not. We do no provide it because we have to, and if the the vendor drops support, we are at their mercy. If your card suddenly stops working, you can blame nVidia, not us.
That being said, we are looking at this from a completely technical aspect. How much work is it for us to include the 9631 driver blob compared to how much it helps users. Note that this isn't just a matter of putting it in. Once we commit to supporting it in feisty, we commit to supporting it over the life of feisty (1.5 years) and probably, much like the native driver, supporting it in later releases of Ubuntu.
The primary loss here is composite features for desktop effects and possibly some performance with GL applications (games). This is hardly a critical loss, but we realize that current trends warrant the use of such features. It is very likely we will include the 9631 for feisty, but the scope of it's inclusion and the existence of it past feisty is still up for debate.