I tweak my Revolution.ini file a lot, so I noticed the change to it with 2.9. Strangely though, whenever it is now generated, it has what appear to be error lines instead of description/comment lines in it about a fourth of the way down or so. For example: "# XML key TXT_KEY_BUG_OPT_REVOLUTION__HUMANINDEXOFFSET_HOVER not found."
Not sure if this is a bug, but it has me a little concerned since I like to play with my Revolutions settings quite a bit and make my settings in this file much more severe than the default.
I had been playing a game where I saw no evidence whatsoever of TechDiffusion (its settings are included in that .ini) in the late classical age of the game, but of course it could have just been an unusual situation and completely normal behavior.
Here's the file (zipped):