Basically, I'm looking for a least common denominator declarative GUI language that would be perfectly suitable for rendering with JavaScript to HTML/CSS, with Python to wxPython and with C# to WinForms... emphasis on the least common denominator. Otherwise, I'm perfectly aware this is almost impossible. Basically, JSON for declarative GUIs rather than data.
Oh yeah, and the real kicker: no XML. Period. Ideally, the syntax would be something like Markdown where it doesn't look like code.
If you don't know of any such thing, you can just post some ideas on what you think it should look like and how you think it should (or could) work, because I was planning on creating one myself. I'm just making sure I'm not reinventing the wheel.