Why not tackle the simpler of the two problems first?

E.g., ignore the HTTP/Swiki stuff for now and just create the local
SquikiPad thingie?  Regarding persistence -- I agree with you that flat
files are the simplest way to share for now.  What file format?  Should
we just use XHTML and extend it with some Squeak-specific tags?

If I were building this, I would assume at first that Squeak images were
the only clients ( but I would use a file format that anyone could
create/edit in NotePad ... )