Nintendo's newest system launches tomorrow. By now, there is very little to discuss about the Switch's hardware that has not already been covered in detail online, though I would like to highlight the excellent technical overviews of both Digital Foundry and AnandTech. Ryan Smith also figured out immediately that the Switch actively converts DisplayPort to HDMI. (I don't like Nintendo's docking implementation, for what it's worth.)
If you're familiar with mobile silicon, it wasn't very hard to understand the Switch's hardware. The key points are that it uses a revised NVIDIA Tegra X1 SoC with a Maxwell GPU, still fabbed on TSMC's 20SoC process. 20nm was unequivocally a bad node. Transistor leakage was a massive challenge on the process, which came just before the transition to FinFETs. Essentially this means that the X1 in the Switch is far from competitive in terms of computational efficiency.
Furthermore, in order to fit its power and thermal budgets, Nintendo had to downclock the X1's CPU, GPU, and memory quite considerably to provide reasonable handheld battery life. Resulting performance is not very impressive to say the least. There wasn't much that Nintendo could do, however, since NVIDIA had nothing newer to sell it that could ship within Nintendo's target deadlines.
Some, namely Apple, were able to wrangle 20nm well enough to take advantage of its benefits, but many silicon vendors stumbled severely with it. To see a game console utilize 20SoC is frankly a bit depressing. A lesser problem is that ARM's Cortex-A57 is not exactly a terribly efficient CPU architecture by 2017 standards. The Maxwell GPU, however, did feature a new, more efficient tiling architecture that was perfectly competitive upon its initial release.
Less known to many is that the original X1 shipped in a rather sad state. NVIDIA failed to make a working interconnect, and ended up shipping broken silicon. The end result was that the four LITTLE CPUs had to be disabled, so only the four big CPUs were actually active in the original SHIELD TV and Google's Pixel C. This did not stop NVIDIA from advertising eight functional CPU cores, however.
New to the Switch is a revised X1 chipset, for which NVIDIA probably removed the four LITTLE cores entirely, and likely replaced the broken interconnect with something simpler and hopefully fully functional. This would be the minimal level of fixes that I hope Nintendo demanded. Beyond that, the revised X1 in the Switch and the 2017 SHIELD TV likely features fairly minor improvements. It's possible that there are differences between the two new chipset revisions, but there is no public information available either way.
1) To be clear, even if NVIDIA is calling both chipsets (2015 and 2017) "X1," if it really has removed the LITTLE cores and replaced the interconnect of the latter, it would actually be a new chipset. It's also worth noting that both SHIELD TVs come with 3 GB of LPDDR4 RAM, while the Switch features 4 GB, an important difference.
2) I was wrong: the A53s are still there, and the logic is still broken. Unbelievable. There's no public evidence of what has changed then, though if I had to guess, there might be some semi-custom tweaks to the GPU and not much else. (Those could be important differences, mind you.) Not making any claims!