With Illustrator being compiled for 64-bit, I'm wondering if the change will break certain third party plug-ins and scripts. There's a few pretty handy ones I'd hate to lose.
Will Illustrator have both 32-bit and 64-bit versions similar to what was done with Photoshop in CS5.5? In the case of Photoshop the separate 32-bit and 64-bit versions were necessary for cutting/copying/pasting content from one app to another, like 32-bit Illustrator CS5.1 or 64-bit After Effects CS5.5. It appears the CS6 suite will still have some apps that are 32-bit only.
Straight to the point: Most plug-ins will require updated versions. the new version has been changed quite radically in some areas, and this may break compatibility not only with the plug-ins thmeselves, but also documents that have references and data from plug-ins embeded. It would be smart to keep your old version of AI around for a while...
I guess that's the main reason why I'm wondering if Adobe will have two copies of Illustrator in CS6, a 32-bit version and a 64-bit version. Older plug-ins and scripts may still work in a 32-bit version, along with maintaining better compatibility with existing .AI files.
It is a shame to lose use of some old plug-ins. I have a few Photoshop plug-ins that have been rendered useless by the move to a 64-bit operating system. For instance, Kai's Power Tools 3 was a pretty fun package. A copule of its .DLL files just aren't compatible with Windows 7. I don't know why Corel isn't making some effort to revive the old KPT filters in 64-bit; they could probably make some decent coin for the effort. I still have an old desktop machine running Photoshop 6 in case I absolutely needed some KPT cheese to throw into a project.