The Shield Tablet does not use Maxwell graphics. It has a single Kepler SMX, amounting to 192 CUDA cores. Maxwell has thus far only been released for desktop and laptop graphics solutions in the 900 series, not tablets. The Tegra K1 chip (the technical name for the GPU) uses the same architecture as the 700 series. The Tegra K1 in the Shield is also only 32-bit, not the 64-bit Denver K1, whereas the iPad Air 2 has a 64-bit CPU. This will give the ipad some serious advantages.
Also, a few benchmarks have already come live benchmarking the Air 2 against the Nexus 9, which DOES have the 64 Bit Denver Tegra K1 (still on Kepler). The graphics benchmarks are pretty neck and neck, so the Air 2 will probably outperform the Shield Tablet, to be honest, but the Air 2 doesn't stream games, so it's all about what you want to do with your tablet.
The only part where Jimbob was wrong was about when the two were coming out. The Shield has already been out for a few months. The iPad Air 2 just came out. The iPad Air 2 has a serious ability to possibly outperform the Shield Tablet as far as regular apps go. The Shield Tablet however can still stream games better. I appreciate your fervor, Ellidor, but truth is, the iPad can and does come close, if not pass, the Shield Tablet. The original discussion was on the original iPad Air, which, I do believe the Shield Tablet is a better value in comparison. With the game streaming, I'd still buy a Shield Tablet over the Air 2, but statisically, the iPad Air 2 is just as strong a tablet to Nvidia's stronger CPU (the 64-Bit Denver Tegra K1) so there's a pretty good chance it definitely can beat the 32-bit Tegra.
If Nvidia comes out with a Tegra K2 by next year with a 20nm, energy efficient Maxwell GPU, I will be very impressed to see what that can benchmark.