Ah, you've just hit on the crux of the problem.

We have a bit of a chicken-and-egg situation for Inkscape supporting those. Firefox hasn't, so even if we coded it there still would be not as much benefit as there would be otherwise.

To help, talking with the Firefox people about rendering them would be a good idea. 

Also... having end users willing to help with defining the task, testing and perhaps even adding a little coding help are some of the best ways to get a feature implemented.