There are already oils out there that would qualify for this viscosity rating, IF it existed.
Look at the specs on different 10w30s for instance. One will show a viscosity of 9.8cst at 100c
(Mobil 1) while another shows 11.9cst at 100c (Amsoil) Both are technically 10w30, however
the Amsoil is almost a 40wt, while the Mobil 1 is almost a 20wt. So if you want a thicker oil,
look at these specs.
I have tried looking at the vis at 40 and 100c to get the heavier oil for my boat. Valvoline sae30 is 11.0 at 100c and Chevron Delo 400 sae30 is 12.5. But yet i notice no change on my oil pressure gauge. Maybe the "thinner" oil flows faster and builds the same pressures???
I don't think most oil pressure gauges are accurate enough to show a small change in oil pressure like that though. Unless you have something like an Autometer oil pressure gauge, you really can't trust what you're reading all the time.