It looks like someone at Kobo tested a new tablet codenamed Macallan last month. It's going to be called the Arc 10HD, and it is running Android 4.2.2 on an 1.8GHz Tegra 4 CPU. But that's about all I can tell you for sure.
I do not have access to the benchmark results (they were removed) so I can't even confirm that this is legit. But the screen shot that I did see showed that this device had a screen resolution of 2560x1504. That's the same screen resolution as on the Samsung Nexus 10, which suggests that the Kobo Arc 10HD is indeed a 10" tablet.
There's no information yet on the rest of the hardware specs, nor do I know when this tablet will be released. Odds are it will show up some time this Fall, but that is just an assumption. Kobo has released new 7" Android tablets in Fall 2011 and in Fall 2012, and I would not be surprised to see yet another 7" tablet show up alongside the Arc 10HD this Fall.
One thing I can add is that this tablet has yet to hit the FCC website. Kobo's new ereader showed up last week, but it has not been joined by the new Arc 10HD.