Hi,

Or rather, avec du Flymake.  I just pushed some updates that allow
Flymake and backends to exchange hints about the modified portions of
the buffer.

This in turn allowed me to build a very simple prototype
flyspell-flymake.el (attached after the sig) with backends that reuse
Flyspell's machinery and turn Flymake into a spell checker.

It is not really usable since it suffers a lot from Flyspell's quirks
like moving the point as it's checking words, a lot of chatter in the
echo area, and probably more that I haven't noticed.  This is mainly
because Flyspell doesn't provide any kind of API, and all I did was
override the overlay API around calls to `flyspell-region' using
`cl-letf.

Still, works better than I expected it to.  If you want to try it, build
a recent master, load the attached file, and eval one of the following

   (add-hook 'flymake-diagnostic-functions 'flyspell-prog-flymake) ; for programming
   (add-hook 'flymake-diagnostic-functions 'flyspell-flymake) ; for text

Then M-x flymake-mode

João