The problem with such approaches is that you have to model all the environmental and performance factors that could cause an identical pseudo-AoA to be calculated, in all flight modes. And to do that you need a range of sensors, all redundant... so now you need additional input validation and sanitisation.

For example, measuring slipstream over the wing is not sufficient. You need to known the pressure ratio between above and below, so there's two sensors. But airflow over a wing is not contiguous or straight, so you need more spanwise sensors to start averaging. And the inboard wing will stall first and give erroneous data, so you need to detect that and disregard it...

Rather than just measuring the raw value at source.