Self shadowing would be something to be done in the 3D rendering engine, inside the part which is in IL-2's native code (il2core.dll).
That part is out of reach for us modders and without wanting to belittle Freddy's attempts, while he might have found a way to work around this and give some impression "like" self-shadowing, he's been unable to deal with the core issue as well.
TD...
They have the sources so they could kick off an attempt to revamp the whole IL-2 3D part to other dimensions, but let's face it:
Besides the knowledge required and the amount of work this would mean, it's highly unlikely that TD is even allowed to perform such kind of upgrades to IL-2, since if they did and if they would give IL-2 the eye candy like newer games have (CloD, BoS), who should buy BoS then and why?
At the end of the day this isn't just a technical issue, but a commercial one as well.
Treat it like "limits intentionally never removed", that'll roughly cover it.
Best regards - Mike