90+% of real-world SVG files display just fine with NanoSVG, just to name one of several small SVG renderers that are already available. And it's not one of those Microsoft Office scenarios where the 90% subset is slightly different for every user.

So I don't really see the point in introducing any new vector graphic formats. Just define a subset of SVG that supports the features commonly in use, give it a name, and adopt one of the existing lightweight renderers, forking it if necessary.

As others have pointed out, representation size doesn't matter because it'll be compressed anyway in any applications where size is important. Plain old text is fine.