I've just published GoBlockly: an interpreter for the Blockly visual editor output written in Go. This is something I wrote as part of a larger project (reimplementing the Belphanior Butler in Go), but it was a reasonable-sized chunk to break off and polish. It passes Blockly's own unit tests and allows for addition of custom blocks.
Example output of a server running GoBlockly library
If you program in go and want to play around with Blockly as a UI for simple code authoring, feel free to try it out! It doesn't come batteries-included (i.e. you'll need to set up your own Blockly web client and send the code back-and-forth to the server in go), but Go makes it easy enough to write a web server that this should be straightforward.