I have today attempted to submit my application, Pegasus Mail, to GMail to go through their "validation process". Clicking the button that said, simply enough, "Publish App" took me to a bewildering, convoluted multi-list screen of different terms, conditions and requirements — even including the demand that I make a Youtube video showing the code operating (seriously?!).
That, while burdensome, confusing and complicated would probably have been manageable — and of course, it's all freighted in terms of "protecting GMail users' data", so you cannot be seen to criticize it without appearing to be somehow irresponsible… But right at the end is the sucker punch — Google will charge you from "$10,000 to $75,000 or more" (their words, not mine) for this, and will require you to go through the process (and of course, pay the fee) annually.