There have been rumors suggesting that the ATV hardware won't be updated this year, or at least in quarter 3 of this year, which would include the september time frame, (but perhaps October is quarter 4).
http://www.appleinsider.com/article...per_quarter_but_no_update_planned_for_q3.html
I'm in the market for a second ATV2 for our bedroom TV. But it's not critical so I'm willing to wait a month to find out. If they don't update this Fall, I'll pick up that extra ATV2 as a refurbished item from Apple.com for $85 (+ tax) with free shipping!
http://store.apple.com/us/product/FC572
We haven't heard any announcements of a media event in September (as far as I know), though that september event has been reliably happening for the last few years, and the month is already halfway done.
If I were a betting man, I'd predict the following: Apple will hold a media event for the iPhone 5 either late this month or in October. They'll spend a few minutes talking about how the latest version of the Apple TV firmware will allow airplay mirroring from iPad2's and iPhone 5's. They'll announce no change to the ATV2 hardware.
The only realistic hardware change I would think people would be interested in for the ATV would be support for 1080p playback. I don't think Apple is in a hurry to add that functionality, though, since they don't have 1080p content available on the iTunes Store. Yes, there is YouTube and Vimeo content that's 1080p. And I would love support for 1080p, since I have young children and a 1080p camcorder actively collecting HD home movies I store on my computer. (there are also people ripping blu-rays, but Apple probably won't publicily support that practice, and they've shown no interest in blu-ray anyway).
But if Apple enables 1080p streaming on the ATV2, it will beg the question about what 1080p content APPLE offers, so I'd expect them to have that question answered before they update ATV2. IE: when itunes movies become available in 1080p.
Just my opinion. I'd expect that ATV2 gets hardware-updated next spring. But I'd love to be wrong and have them update this Fall.