http://jsfiddle.net/ericwilligers/e2csv0o8/ The specified transform-style serializes as 'preserve-3d' for both a <div> and an <svg> element. However, the computed style is only reported as 'preserve-3d' for the <div> element. The <svg> element computed style is reported as 'flat'. Spec: https://drafts.csswg.org/css-transforms-2/#transform-style-property
Safari, Chrome, and Firefox all agree on rendering for this test case. I don't believe there is any remaining compatibility issue.