It's likely OEMs will surpass Nexus 10 before its successor debuts. I have a feeling that Samsung will announce Galaxy S4 and a couple of tablets using Exynos 5 Octa in a few weeks. Snapdragon 800 and Tegra 4 tablets should hit fairly soon as well (IMO), surpassing Nexus 10 in almost every aspect except the prices and "pure" Android experience.
Nexus 10 is currently the king of 10" Android tablet and as much as I wish it had a bit better design, I don't see it getting updated when there is no competition at the moment. (Though a product like Xperia tablet Z has other virtues than pure performance) Plus, Google don't seem to be fond of announcing products ahead of actual shipping dates, so I wouldn't bank on them making announcement of upcoming products.