>Guido also happens to be working at Dropbox, but I don't know if he's directly involved with pyston or not.

With the proviso that a lot can change in two years, here's a relevant comment from the Dropbox Pyston announcement [1]:

"Guido's advice has been extremely helpful, but so far we haven't been able to get any code from him"

[1]: https://blogs.dropbox.com/tech/2014/04/introducing-pyston-an...