I'm pretty sure Ted and/or Dan (maybe?) did a Hypercard-alike in Squeak a long time ago. It really can't be a terribly hard thing for someone motivated to do in Morphic these days. We have a variety of useful capabilities to interface with OS facilities and can drop files on windows etc. We can even do multiple host windows now. On Mac and I think Windows we can do host menus.
If you like HyperCard, get on and make it. I bet it would even be possible to read in a lot of original stacks.
tim -- tim Rowledge; tim@rowledge.org; http://www.rowledge.org/tim Strange OpCodes: KFP: Kindle Fire in Printer