The LTE version of the Nexus 7 2013 just started shipping to the US last week. If a week of running on a stock ROM is entirely too long for you, take heart: even while you read these words, modders and ROM developers are hard at work building all kinds of aftermarket goodies for your unlocked tablet. That's because Google just posted the first full factory image plus binaries for the new model.
This build of Android 4.3 is marked as "JLS36C" (the over-the-air update that was released almost immediately) and the AOSP code is marked as "android-4.3_r3" on Google's code hub. That doesn't mean much for end users, but it could indicate that a slightly updated Android build is very close for the rest of the Nexus line and Google Play Edition phones. At the time of writing we haven't found anything that implies any new user-facing features within the N7 2013 LTE image.
The image gives Nexus 7 LTE owners a clean slate to flash back to. And now that the binaries are out, you can expect to see ROMs based on the stock build and modified AOSP versions popping up on your aftermarket forum of choice. The factory image comes in at a whopping 376MB, so don't download it on a tiered data plan.