The original Mobil 1 synthetic, which has been around for years, is rated for 15,000 miles so it's not too difficult to imagine that with continued product development that another 5k is possible.
The testing for Mobil Annual was done on modern (2015-2016) 4 cylinder turbo engines. They were torn down after 120K miles with 5 oil changes performed at 20k intervals and all high-wear parts checked within specs of new. But as
@Frankenchevy mentioned, these little 4-bangers are different animals than our older tech engines.
I switched to synthetic in my square for a while but it seemed to leak more than usual so I went back to conventional. The heaviest weight Annual oil you can get is 5w-30. I think if I put something that thin in the 'burb it would all leak out before I had a chance to drive it!
The biggest issue for me though with 20k mile oil is this, even if I had a newer vehicle with modern engine internals and no leaks, what oil FILTER is rated to go that long? The filters in my dd Hondas are ridiculously small. There's not much media filter in them so the odds of them catching and holding a year's worth of dirt is slim to none.