With SVG you first have to parse the file into a DOM, because otherwise you can't really apply CSS (for which you of course also need a parser). On this way you avoid all the common XML pitfalls like xml entities blowing up your memory. If you want to show animated SVGs you need a javascript implementation, because half the browsers don't understand the animate-elements. Being able to include javascript probably is the reason why most image hosters don't host SVGs. Javascript in SVG opens doors to all kind of evil things like cross site scripting. So you walk down your SVG DOM and begin to parse path data strings. The syntax seems understandable after a short while so you think you can easily write a parser. But the parser you'll write will be wrong because the details of the syntax are totally arcane, whitespace can sometimes be dropped (e.g. A.5.5.5 10.5.5 is the same as A 0.5 0.5 0.5 1 0 0.5 0.5), commas are allowed at some places but only one at most. Every program supporting SVG got this wrong at least once, and some like Inkscape still have a buggy parser. So you look up how to render this path and you see that you just have to render the border, but there are gazillions of options how to render borders you all have to support. So the next element you want to render is a text element, which is a huge joke because it doesn't even support multi-line text, but silly things like text whose baseline follows a path [1]. Because internationalisation is important SVG files of course can show different things depending on the locale [2]. So afterwards you just have to apply filters, which are basically half a pixel based image manipulation program [3].
I really don't see how adding new features makes any of this easier, when SVG 2.0 is basically a backwards-compatible superset.
To proliferate vector graphics on the web we actually need a way simpler flat format. The only thing you actually really need is bezier paths and a way to fill them.
[1] http://www.w3.org/TR/SVG11/text.html#TextOnAPath [2] http://www.w3.org/TR/SVG11/struct.html#ConditionalProcessing [3] http://www.w3.org/TR/SVG11/filters.html