Update: I just released the first Google Compute Engine Debian 7.2 image, built on 2013-10-14.
As I mentioned before, Google Compute Engine will add the necessary support that will allow Debian's kernel to work. One noteworthy choice is that the virtual hardware will be pretty modern. This will allow the best performance and feature set, and the chosen hardware is already supported by wheezy and newer kernels.
Unfortunately, the squeeze kernel doesn't support it, and squeeze-backports kernels are updated by the Debian kernel team on a best-effort basis (e.g. as of 1-2h ago they hadn't yet updated it for 7.2). While it's good for build-debian-cloud to retain support for Google Compute Engine squeeze images via the backports kernel until squeeze's end-of-life, I think we shouldn't ship official prebuilt images with a best-effort level of kernel security support.
Therefore, I propose that we (1) deprecate Google Compute Engine squeeze images; (2) once the relevant Google Compute Engine feature launches, document on the Debian wiki how to build a squeeze image for Google Compute Engine with the backports kernel; and (3) keep the functionality in build-debian-cloud at least until squeeze moves to archive.debian.org
. Wheezy images will continue with the same levels of support from Debian and Google as they have now.
Let me know if you have any objections. Unless there's a reason to do otherwise, I'll wait at least a week, and then I'll mark the Google Compute Engine squeeze images and older wheezy images as deprecated, using Google Compute Engine's feature for that, pointing to the now-current wheezy 7.2 image as the replacement. The images will continue to work for now, but will warn about deprecation.