Exactly, your position of "not possible" didn't see his MillersOil yet. So you were fundamentally wrong, weren't you? Shear stability in a rather Newtonian 0W-20/20 happens to be zero issue. A density limitation might be...
Feasible in general, just a 0W-20 of elevated HTHS. I was adressing the beginning of the thread here. With pursuing the low density it would become unnecessarily hard, as we made clear already.
But there's at least two problems I actually pointed to: Not only will a higher density 0W-20/20 walk towards maybe HTHS 4, there's also the problem of simply no data to be had from just VI regarding a temp of 150°C as soon as we can allow advanced VII strategies. Think of the rubber balls etc. to intrude if you will: https://bobistheoilguy.com/forums/threads/steven-armes-rubber-balls.328048/
HTHS eats like half of the boosting, but not all.
No, the 0w-20 he linked to did shear or the HTHS viscosity would be 2.9 cP but it was only 2.7cP. Which can mean anything between 2.65 and 2.74 cP too. It's a normal loss of viscosity for just about any oil with stay-in-grade requirements.
If you add viscosity improver to the above oil to get to the 40C and 100C viscosities you will fall well short of 3.5 cP. Don't know how much higher you want density to get unless you invent an oil that sinks in water... The oil I gave viscometrics for above is already impossible as the base oils don't exist and that was a best case scenario. The oil you are proposing is even harder to make.
Bottom line is the Millers is a run of the mill 0w-20 oil, nothing fancy about it. If we limit ourselves to existing oils, the highest HTHS 0w20 I've come across is Redline, and that still only makes 2.9 cP or A5/B5 viscosity requirements, because it shears aswell. It needs VII to get these viscometrics.
With todays and even tomorrows technology, it's not possible to make such an oil. Maybe PAG based, but those would not be mixible with existing ols so not suitable for engine oil use