I like the librsvg approach of just supporting the important features. Then again, you can't do custom fonts (which is an issue for me) and I guess everybody has features they need / would like.
librsvg can render into different backends via cairo. Maybe with a little more work the combination of them could form the library you're talking about? I definitely agree about having a good library. The way everything is deeply bound into inkscape is a real shame. And when you use something like chrome (blink) you kinda need the whole kitchen sink to make it work.
At a guess the reason it is minimal is because there wasn't much dev work on it for a long time. If other devs had turned up and added missing features they would have been added.
Also; newer features like meshgradient haven't been in Cairo for very long.
Afaict Features get added in unescape as its open source, a soft of neutral ground + with authoring capability and artists in the community making it easy to demo proposed patches.
librsvg can render into different backends via cairo. Maybe with a little more work the combination of them could form the library you're talking about? I definitely agree about having a good library. The way everything is deeply bound into inkscape is a real shame. And when you use something like chrome (blink) you kinda need the whole kitchen sink to make it work.