Without slack labor markets, particularly for those with bachelors degrees but no non-teaching professional training, the whole ed reform edifice falls apart. Everyone leaves teaching, and that's that! For the past, what, seven years, the idea that someone with a BA in English, History or education was generally employable has seemed increasingly fanciful. I'm not betting on a tight labor market, but it is at least conceivable now. TFA is the canary in the coal mine for this phenomenon.
The first Achilles heel of course is just kids, with parental support, refusing to take the damn tests. I'd note that the whole "opt-out" conversation is still quite moderate. Once you hear "strike" and "sabotage" (And let's be clear, sabotage is real easy here. Kick out the plugs. Tear the test, etc. Answer everything "A.") displacing "opt-out," things will be getting real.