Since most of the code is hidden away inside a DLL, it's pretty much impossible to adjust stuff e.g. for a newer version of Unity or special use cases.

Are there any plans to release the source?

We're not planning on releasing the source at this time—but definitely want to make it extensible enough for lots of different use cases!

So. How much would you want raised as a Kickstarter to open source the whole thing? :-)

It makes me sad to use code I can't modify or learn from... :-(

I hope it's clear, and that it helps, that at least all the .shader and .cginc files are readable! Meaning, the bits that actually go to the GPU and do the raymarching, you can read (and modify to your own purposes).