You don't need a GUI or expensive programs to make very stunning and impressive graphics. I've coded SVG manually myself (using Jade templates) and I've written TikZ and asymptote and it works very very well. Remember, we are programmers and not graphic designers who need Illustrator since they often don't code.
Check out some stuff they do over at tex exchange:
You can also easily take existing SVG and extract the curve formats out, normalize them and integrate them in your project as a few arrays. You wouldn't start from scratch and have to redraw the github logo. You just put it into source code and things such as arrows you can draw with a few commands
They don't care. Designers don't care that you can code SVG manually yourself. They use Illustrator because it is the best software to do what they want. You need to respect that this is how designers work if you want to be taken seriously by designers--and that's step one of changing anything.
If it requires a text editor, you just lost 95% of designers (conservative guess) and you won't get them back because you've shown that you don't respect how they work.
Illustrator and related formats - EPS, AI - are considerably more featureful than SVG supports. They are able to mash their documents down to SVG, at the cost of losing data. Which nobody will do for raws.
And, as is so common with open-source attempts at graphics software, nobody takes Inkscape seriously. Sorry.
I don't say that designers should program instead of using their tools. What I say is: Stop the craziness of 50 different projects which give you some set of icons. Each a little different but each repeating things over and over again. Let's define one framework and go from their and satisfy 95% of all projects.
Let's stop the craziness of 50 different programming languages which all bundle slightly different sets of features. Can't we just put all the features in one language?
The reason to use one icon set on a web page is that the icons look good together. Putting a bunch of different icon styles in one set defeats this. A good designer has the skills to bust out Sketch and make another icon in the same style if they need it, and then contribute it back to the set for consideration.
If you're not able to do this, there's always http://icomoon.io/app/ which lets you bundle icons from different sets into one font.
And who, among the people who actually design and build icons, would care?
Hint: they use Illustrator. They're going to keep using Illustrator. They're not going to stop using Illustrator so you can have a marginally easier Github workflow.
Check out some stuff they do over at tex exchange:
http://tex.stackexchange.com/questions/tagged/tikz-pgf
You can also easily take existing SVG and extract the curve formats out, normalize them and integrate them in your project as a few arrays. You wouldn't start from scratch and have to redraw the github logo. You just put it into source code and things such as arrows you can draw with a few commands