full screen video button?

One minor point of clarification, Cathy.

Vimeo does not seem to be stating that IFrames are legacy constructs.  In fact, the IFrame tag is very much a part of the HTML5 standard and continues to be supported by all major browsers.  Vimeo seems to be stating that browsers no longer allow full-screen functionality to be implemented within an IFrame.  I can't confirm the accuracy of that statement, but I'm sure Vimeo knows their stuff.

This is a subtle difference and is of little help to you, but it illustrates the difficulty of a fix, since IFrames are used (and will continue to be used) extensively throughout Internet architecture.

...and for what it's worth, I can't seem to make Vimeo videos play full-screen in Adobe Captivate, Lectora Inspire, or iSpring Presenter either, though I'm no expert in any of those tools.