Right now there are several packages in Debian GNU/Linux that duplicate the scintilla code; at least scite, anjuta, qscintilla and geany. It would be great if you could turn scintilla into a shared library (at least on Linux) that applications could link against. At least the Anjuta project doesn't like embedding scintilla and would like this:
This would require defining a public API for programs interacting with scintilla, creating and tracking an ABI number from that. Some good information about API/ABI and libraries from Debian's perspective is here:
Here is a guide from GNU about libtool:
If you are not interested in turning scintilla into a shared library, adding a static library might be useful to those who currently embed scintilla code.