Clearly it'd need to be very transparent to airflow—something like the face guards of an NFL player—a heavy gauge titanium cage or something like that.
Btw, the Wright Bros knew the importance of AoA and included one on the Wright Flyer. Implementation? — a length of straight stick parallel to the wing chord with a bit of ribbon affixed to the end :-D (KISS at work!)
i.e., on some systems I've worked on, we had a range that a sensor was expected to be in (normal, just do regular control loop), an outer range that was unlikely (stop reporting for a while/hold control output constant to see if it gets better or worse before warning operator), and a narrower range that was flat out impossible (notify operator of sensor failure/put system into a graceful shutdown).
I assume that the engineers designing this system had something similar, but given that MCAS activated with an AoA indication of 80 degrees (IIRC) and that's essentially impossible on a 737 (or at least would correlate with a hell of a lot of other warnings), was there anything they could do to warn the operator (pilot) that there was likely a bad sensor input?
Not sure if you caught this post https://philip.greenspun.com/blog/2019/04/08/boeing-737-max-... which I think is basically the same idea as you are suggesting.
From all outward appearance it appears they failed to do any kind of range check On the data. Although people were quick to point out that AF447 had a situation where the airspeed decreased to such a low level that the warnings stopped (because it was outside of any normal flying range) which was implicated as a source of confusion.
Air travel is very safe because of literal generations of engineers working hard to make it safe, in this case the failure is one of procedure and people been people (cutting close to the wind on what was allowed).
Things usually tighten up after this kind of thing and then gradually loosen until the next disaster that could have been preventable.
it would probably just get blocked then by bits of bird.
Seems like a bad idea to use mechanical vanes for this, especially if you're going to bet the whole farm on a single instrument as Boeing seems to have done.