Update 2: According to Shake users who have contacted Apple regarding software maintenance issues, Apple states that users will be unable to receive further updates for Shake as development has been focused towards the "next generation" of the application. Partial quote below, with full quote in the thread.
Apple will no longer be selling maintenance for Shake and no further software updates are planned as we begin work on the next generation of Shake compositing software.
According to our source, this "next generation" program is not based on Shake code, but rather is based loosely on Motion code, which may explain why Apple is licensing Shake code to select Maintenance customers for $50,000.