I am not any kind of engineer, but have wild ideas about putting a bunch of sensors on a board with a connection to a data-logging device. Sensors would just give relative position. The data could then be processed to give a sort of movie of board flex as it's being ridden, available to analyze any which way. Add to it some accelerometers and you could get some idea of pressure distribution, and GPS data to get an estimate of path of center of mass. Then you'd have a data set you could maybe do a lot with in terms of board response.
I even looked at suppliers for sensors that might be suitable, but it's still at pipe dream stage for me. I wonder if ski manufacturers already do such things, or have blow past armchair stuff like that long ago...