Michael @cycomachead already bugged me about this one:
We should have a fork of scratchblocks for these forums, implemented as a Discourse plugin.
Anyone want to work on this? If someone wants to figure out the Discourse part, I'm happy to make the necessary changes to scratchblocks to include the Snap! blocks by default (basically just need to modify commands.js). 
Thanks for posting this!
I don't have the dev time for this, but I'm happy to answer any questions or give others pointers!
I think we want a widget: https://meta.discourse.org/t/a-tour-of-how-the-widget-virtual-dom-code-in-discourse-works/40347
Maybe this is something we could throw a 12-year-old at, without Jens getting mad at me.
without Jens getting mad
Is that normally a concern?!
Jens would really be happiest if nobody else touched his code at all, and he especially doesn't like me to solicit contributions widely, e.g., among you guys, or among Berkeley students. (He does end up happy, even enthusiastic, about certain individual examples.) He says he spends more time vetting someone else's code than it would take him to write it himself. But Discourse isn't his code so he wouldn't care about other people in it.