How difficult is it to obtain a professorship with a MA in TESOL?

I'm currently an ALT with time on my hands. I'm looking to at least double my current salary. I feel like getting an MA in TESOL would be the quickest way to go, especially if I take courses online. What are my chances of at least a non-tenured position if I have roughly 10 years of experience teaching English in Japan? Any advice appreciated. Thank you for your help.