This discussion is delusional in terms of not seeing the obvious. A little upthread, I displayed this chart of the QBO winds in the context of adjacent stratospheric winds.
Directly above the QBO in altitude lies the SAO winds of the upper stratosphere. Not surprisingly given the acronym, these are **S**emi-**A**nnual **O**scillations in wind speed whereby the wind reverses *twice* each year, which means either the sun passing nodally over the equator is the trigger for reversal, or it could be that the trigger is the sun at its maximal absolute declination to the equatorial plane. So whatever the detailed mechanism of the trigger is, it's **certainly** not some resonant behavior caused by a "aeroelastic spring-mass dynamic" as you suggest. Rather, it's obviously an orbital trigger -- which is obvious in the sense that you wouldn't be able to show even a slight long-term divergence from a semi-annual synchronization, if you wanted to try to debunk the model.
Thus the QBO is just the SAO with the added trigger of the lunar nodal cycle becoming stronger for the higher air density at lower altitudes. Taken together, the two models are both plausible and parsimonious.
I could argue this **extremely** quantitative model until the cows came home and it still won't become accepted because it apparently diverges from the script that climate researchers must follow, which is to assertively ascribe a resonant mechanism to a behavior and never mention a lunar mechanism (perhaps so as not to embarrass colleagues?)