Creating flat packages should be easy enough, I'm hoping to experiment with them during the sprints at EP (but we're already at the end of the first day).  At first I feared that creating installers in the new format would require using GUI tool, but it seems that the creating can be scripted using command line tools (like pkgbuild).

According to <http://s.sudre.free.fr/Stuff/Ivanhoe/FLAT.html> flat packages were introduced in OSX 10.5, which would mean we could only move the "intel" installer to that format.  

It would IMHO be worthwhile to do that for all new stable releases (2.7.x, 3.3.x and 3.4.x), while at the same time further reducing the visibility of the 32-bit installers (as those should only be used by users that just cannot use the newer installers). 

As to the question of actually signing the installer: we ask the PSF about acquiring a developer account once we have something that can actually be signed.