Oh, I know it would be a serious undertaking (I'd probably try hacking it into fish, because I've looked into it's code-base). I was just wondering if it's hypothetically possible, and why no-one has done it :)
EdiX
I don't know. The reason I haven't done it is because it's too much work, there is no pleasant way to do GUI programming and I don't have a clear design for how the UI.