BREAKING NEWS: The Raspberry Pi Linux framebuffer driver has been updated and the PAN_DISPLAY function mentioned in Part X has been added - so the smooth double-buffer page-flipping animation should now be possible without further hacks!
Based on a quick test it works fine - will get back with a confirmation after some more testing...
UPDATE 2014-09-10: Well, the pan (and set virtual info) now work fine but it appears that the vsync functionality does not. Also it looks like there was a change made somewhere deeper in the software stack and the mailbox interface based version does not have the vsync anymore either.
UPDATE 2015-01-06: new info