Indeed, the Green Dot model calls for teams of teachers to be actively involved in hiring their peers; this is a highly-vetted workforce operating in an environment that emphasizes collegiality and professionalism. Without such healthy school envirnments, unions and teachers will have a hard time giving up the tenure protections they've won because of a very real history of adminstrative overreach.
I see this issue as being very similar to online education. My department has a very strong online graduate program. Contrary to all predictions, moving education to an online environment takes a lot of work and isn't as effective at improving productivity as one might imagine. It's possible to do a high quality online program, but it sure isn't inexpensive or easy.
In the same sense, the idea of removing tenure and leaving effective (albeit different) schools has a lot of the same properties. By increasing teacher empowerment, involving teachers in decisions, and increasing compensation you can develop a workable model. After all, tenure is a job perk and it can be replaced by other job perks like employee autonomy and empowerment.
But what the removal of tenure isn't is a cheap way to reduce teacher salaries while holding quality constant. I am agnostic as to the existence of tenure in a workplace. It is a nice perk but it brings downsides as well. What I find more alarming is the effort to remove tenure and replace it with . . . nothing. Or, even worse, replacing nuanced teacher review with test scores (and then removing tenure).
I admit to being very sympathetic to empowered workplaces. My natural work environment is likely the Left Coast and reading about the corporate culture of Silicon Valley convinced me that I'd do better there than in Boston. But these environments are not a cheap and easy substitution for conventional models. They are hard to develop and really require that the employees be either mobile or empowered.
Is that a goal reformers really want to work towards?