I got a response from Todd Courtois:

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Hey Daniel,

I don't know for sure, but I might have the sources to
NH 3.x laying around on a hard drive somewhere. I'll
try to dig those up in the coming months (I'll put it
on my long to-do list). Since Spyglass bought
AllPen, and then OpenTV bought Spyglass, and then
Apple cancelled the Newton, and then OpenTV
floundered, I doubt if there's anyone in corporate
America who really cares whether these sources are
released.

It is remarkable how much post-cancellation activity
there has been in the Newton community. I don't have
much contact with Apple anymore, but I wonder if
Newton activists could convince Apple to open-source
the newtonscript/applications layer of the Newton OS.
It'd be an interesting project to glue that nice
application environment on top of, say, embedded
linux.
Then you'd have a device OS that could compete easily
with Symbian, BREW, PocketPC, Palm, you name it.

Todd
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Please, please, please!!