If you put "Pathfinder" on there, you should probably add "Labyrinth Lord" too (as far as I know, it was the first big-name OSR game).
This is very good looking! I would suggest that you add "D&D Essentials" to the "Fourth Age" era. I'm of two minds about the inclusion of Pathfinder. While I did giggle to see it, and I do agree that it is a spiritual successor to D20 3.5, it is also not "D&D" any more than Labyrinth Lord, OSRIC, or any of the by now dozens of retro clones, variants, and alternate (yet still technically unofficial) versions are D&D. If you include one, as the above comment shows, you open the floodgates for everyone to chime in with "my fav too!". If this were the "Ages of RPG: A Timeline" I'd be fully supportive of including every game that ever there was, however that would require a truly massive image... :-)I would also like to suggest that you create a separate track for more people-related events like the "Gygax leaves TSR" event you included. Things like Arneson & Gygax's death, the addition & departure of several very influential people (Kuntz, Ward, Cooks Monte & Zeb, Greenwood, etc.) within TSR/WOTC, and other such events.Also, to your "red seal" company track, you should add "Hasbro buys WOTC" (this certainly had and continues to have a great influence on the behavior of WOTC & the future of D&D.
Pathfinder is the only clone that actually competes with (arguably beats) official D&D at its own game. That makes it special.
Nice. One minor change I'd like to see is to indicate when the 3 books of AD&D were released. The MM was out for a long time, then the PHB, and then it was another long wait till the DMG was out.