I appreciate the ability to mitigate extremes of chainline angle using multiple chainrings, BUT there are a couple of subtleties of these 1x drivetrains, and a few advantages, which make things VERRRY interesting in a technical sense that looks toward the future.

Firstly is the X-Horizon or non-slanted derailer parallelogram of all unexpected things. Warning, long sentence here: This takes the vertical motion out of the parallelogram, and is allowed by using a very heavy offset to the cage's top pully mounting position, which handles all of the chain-gap motion without making the derailer susceptible to moving inward in response to bumps in the road, and does so using only the lightest imaginable return spring, for lighter shifting feel and less friction in the cabling.
Use of this non-slanted parallelogram with fixed mounting pivot (B-pivot) does not allow for multiple chainrings!

Secondly with the single-chainring approach is the guarantee that as the larger cogs are selected, the chain angles away from the larger cog's teeth at both the "top" and "bottom" of the sprocket, as the cage's lower pulley is positioned a bit "outward" from parallel to the plane of the rear wheel. Result here is that now they can use dished cogs with narrower spacing and still allow clearance for the same old chain width! So expect this 12s cassette to fit on the contemporary 11s XO-type "driver" (freehub body). This is a really big deal, since further extremes of chainline angling are avoided(!!).

Functionally, 1X drivetrains are simpler to operate in extremes of terrain and during extremes of rider effort, such as racing.
Stoners too will no longer have to struggle to remember what chainring that they last shifted to.

The 1X bike is indeed a simpler machine, and potentially lighter, more reliable, and less expensive, not to mention having a cleaner look.

Another good feature of this 1X12 system is that it is still adaptable to just about any old bike, with the dropout spacing only needing to be adjusted to the current standards that all of better componentry has been designed for over the last 25+ years. The trend toward disc brakes may make for less availability of built wheels for our old bikes, but rim-brake wheels can still be built as always.
Note also that cage-to-ground clearance issues when designing around such large cogs are mitigated somewhat by today's larger 650b wheel size and by the derailer cage's no longer having to be so long as to take up slack from multiple chainrings, all of which adds up in this new system's favor.

I don't have any idea what the patenting situation is with all of this stuff, and to what extent this might limit Shimano's ability to exploit these technologies such as the X-Horizon derailer and the variable dished-cog spacing, but so far Shimano has at least come out with a good 1X chainring of their own design to best retain the chain without any sort of chain guide in front.