The blood on the windshield when you are hit is actually a part of the plane's skin. When the damage model records that a particular part of the plane has been damaged, the regular texture for that part is replaced with the damaged texture. So for a pilot wound, the regular windsheild is replaced with a bloody one.
What you are asking for would require every gauge, and every panel... in every plane... to have a bloody version. I just dont see all the textures in the game being redone. Not to mention, it would mean everyone would have to RE-download all the skins just to impede their vision when they get shot. No thanks
THIS INFO IS CORRECTED IN A FEW POSTS DOWN... MY MISTAKEAs for gunsights... those are kept on your local machine... and with all the custom ones out there, there is no way that I can see to make them bloody when the pilot gets wounded.
Not to mention... I personally think the blackouts are bad enough.