It's not that no one is interested. I garuntee if the platform was supported there would be developers. However it's been long enough for those that know. That Scirra doesn't build the bridges. I've been on the forums for 2/3 years and I know Scirra has never built the bridge. They are 100% backing pure HTML5 supported by Chrom and will show support for other 100% browsers.
As for your link. Unfortunately languages aren't magical. WebKitC# doesn't mean it works for the Vita. It's just a C# version of WebKit. However platforms and specifically custom hardware and software platforms have lots of nuounces that are specific. There is no way to just plop WKC# and compile for the Vita. Some one would need to go through the source code and make changes to program for the Vita nuounces to make it work. And if some one has to do that anyways. Might as well just use the C++ version which is probably kept more update date by supporting community.
Now could someone get C2 running on Vita. Yes. Someone could go through the effort. Yes. You could take up the mantle of building a micro browser layer and get C2 to run. However like you most of the developers here are like you. They aren't technical enough to write that mirco browser layer. And for those programmers that are technically minded(such as myself), I use C2 to avoid doing that technical level of work. I want to be more productive on the games rather than spend half a year just to power a game on a piece of hardware.
If you want support. I suggest mailing Cocoonjs and asking Vita support. You can go to the Ejecta group and see if someone is willing to make a branch for Vita. Or just ask Sony if they can like Nintendo create a version of WebKit for Vita and PS4.