I wish they outlined a plan to push this icon out to Stable. Even better the plan should call for the browser to eventually refuse to submit forms with password fields unless HTTPS was used for both loading the form and submitting it.

I think that developers who are still using HTTP with passwords either don't understand the implications (and a tiny icon won't help), don't care, or don't have "management buy-in" to spend the time to fix it. Having the browser force best security practices will benefit them and everyone using their websites.