The Android.com site got a very nice redesign, which once again shows Google's commitment to being a lot more design-oriented from now on. On the home page it has an image of a phone and a tablet, both running Android 4.0. So a lot of people have been wondering if that is a Nexus tablet there.
I think this speculation based on this image alone isn't a very good one. First of all, the phone itself doesn't even look like Galaxy Nexus, and it lacks the virtual buttons at the bottom. So you can't really say that if that phone was a Nexus, then the tablet must be a Nexus one, too. Sure, they do have similar design styles, but that doesn't mean much. It just means they are both renders meant to look similar. So I think people are reading too much into this rendering.
If Google had a Nexus tablet to show, they would've probably shown it at the Android 4.0 event, and it would've been made by Samsung. But this wasn't the case, and it would be a little late to show it now. If they really wanted to make one, I guess they could show it at Google I/O next year, running Android 4.5 or whatever (Jellybean).
But will Google ever make a Nexus tablet? It's certainly possible if they think the tablet market is even close to being as important as the smartphone market, and they want to keep the manufacturers in line. But I'm not so sure they would really need it. Most manufacturers are already using the stock version of Android on tablets, and they are updating them pretty quickly. Plus, Google is buying Motorola, and they can just show stock Android on all Motorola's devices as soon as they buy them, and that includes tablets as well.
So they wouldn't really need a Nexus tablet. In fact I think they will even try to relax a bit with the whole Nexus thing once they buy Motorola, since as I said Motorola will give them everything they want and they will make Motorola's devices however they want. Nexus wouldn't really be necessary in that world. So until we get some hard proof that Google is building a Nexus tablet, I would take these rumors and speculations with a huge grain of salt.