In our tests (scrolling an older iPhone on a page with 300 links), we found that it’s actually not as much an issue as you might think, particularly because none of the shadows use a spread value. I’d definitely be interested to see if you have evidence to the contrary.

That being said, it’s definitely something worth considering, particularly since iOS 8 now implements descender-aware link underlines now. If there were a way to duck type for this feature, we’d definitely disable the JS anywhere we detect it working. Drawing an underlined “g” on a canvas and then reading the pixels at a certain location may work, but we haven’t tried it yet.