@Devon: TrueType GX has been suggested as a good starting point as a variable font technology for the web. Indeed, as you pointed out, there is even some lingering support for Apple’s variable font mechanisms. (In case you haven’t seen it, Adam Twardoch from FontLab recently posted some video of the Apple font variation stuff as it worked in older versions of OS X, including with Skia: https://vimeo.com/120047887)
I would say the main issue with resurrecting the old format is that it’s, well, old. In an ideal world, there would be all kinds of improvements that could be made that were impractical, impossible, or just not imagined yet back in the 1990s when the format was born. On the other hand, it would be much more practical, politically, to get more people on board with something that already exists (and was partially supported) than it would be to start from scratch.