From #3820 “Aviation Week: Boeing Expands MCAS Demos To Speed Lifting Of 737 MAX Grounding”: There is not a single mention of SMYD, obviously Boeing cannot allow the stick shaker to still be driven by an invalid AoA. Boeing would not need to mention SMYD if, for the MAX, they had changed AoA processing and supplied AoA L & R data from the FCC directly to the SYMD via the ARINC 429 bus. It would make sense to do the processing only in one system and may help with CPU loading.
The idea that the invalid AoA problem is a fault, or different faults, in 3 AoA sensors seems to me to be very unlikely, purely from a consideration of reliability figures. AoA sensors are very reliable, from satcom.guru on 28th March:-
Reliability of the AoA sensor was evaluated over a 4-6 year period, with a mean time between unscheduled removals was 93,000 hours. A typical airframe is modeled at about 100,000 hours, so the AoA vane typically last nearly the lifetime of the airplane.
As has been suggested in an earlier post, there could be vulnerability in a new harness which causes a short circuit on a resolver signal. Or (back on my favoured suspect) a latent software fault which affects the processing of the AoA data.
There is an anomaly in the FDR for ET302 (Preliminary Report, page 26) at 05:38:42. It seems to show the Control Column L was pushed forward a second or two before Stick Shaker L started! This could be because the SMYD, if it gets its AoA data from the FCC, is running a cycle behind the FCC. Or it could just be an aspect of the ARINC bus data rates. If I recall correctly, there are various data rates available, and a fast changing control parameter going from one system to another (such as Control Column Position) would go at the fastest rate. A slow changing parameter only for diagnostics (such as Stick Shaker) would go at the slowest rate.