In other words, this group of developers has been attempting to implement SVG since the W3C started developing it, and hasn't succeeded yet.
Actually, our SVG implementation is almost complete, only lacking a few things. I believe that the most important and substantial thing that we still do not support are the animation tags. As Inkscape is nowadays a drawing application (not an animation app yet), then I think it is not reasonable to say that we haven't succeeded in SVG implementation yet. We have solid support for the subset of SVG features that are needed for a drawing app. And this subset is substantially large.
You can expect to see animation support in some future version, and then we'll probably see an Inkscape 1.0 later, when the standard finally gets fully implemented.
A list is only as strong as its weakest link. -- Don Knuth