We've talked about this before, but never ask for ETA's on software. It usually leads to buggy software, which you definitely don't want. JBQ, or Jean-Baptiste Queru, said a few weeks ago to never ask about ETA's over on Google+ so he's just reiterating that today.
You may have noticed that the factory images for the other Nexus devices are available for Android 4.3. But so far, nothing for the new Nexus 7, also known as "flo". Jean-Baptiste Queru stated today that there is no ETA. For those that don't know about JBQ, he's the guy with the beard in charge of AOSP and the factory images. JBQ also said "I don't know if they'll ever be available at all." Which I certainly hope is not true. Since I love flashing ROMs and always forget to make backups, it's nice to know that there is a factory image out there I can flash to fix all the problems I may have. Or just to get back to stock.
Before you get to upset about all of this, back when the Nexus 4 launched last fall, the Android 4.2 images for the Nexus 4 were no where to be found as well. But now we have images for the Nexus 4 including the JWR66V build which is Android 4.3. So I'm sure they'll come eventually. The factory image I'm really worried about is the Nexus 7 LTE. If that is indeed available then we'll know the new Nexus coming this fall will have LTE and will be fully AOSP supported. Which was a major drawback of the Nexus 4 last year. Even though it technically does have LTE support.
We've seen a handful of missing factory images in the past, but normally that's due to CDMA technology with the Nexus S 4G and Galaxy Nexus on Sprint and Verizon. But since the new Nexus 7 doesn't use CDMA technology at all, that won't be the case this time. It'll likely be another reason, if the factory images never become available. Either way we'll be sure to keep everyone posted, as we always do. You can find out more information from Android Building, which is their Google Group.