I have verified that After Effects no longer fails to launch on Apple OS X 10.10 Developer Preview 3.1.0.
I am able to launch the app, save a project, quit the app, re-launch the app, and open the saved project.
Fix verified with AE CS6 (11.0.3.6), AE CC (12.2.1.5), and AE CC 2014.0 (13.0.0.214).
It is now OK to start testing and reporting bugs to Adobe, that are specific to After Effects and Yosemite.