The latest version of Scintilla has many more filetypes supported than the version currently used by Geany. It's not that hard to port Geany over to using Scintilla 1.75 (I was able to do it this afternoon in about half-an-hour after poking around). This doesn't provide the filetype information used by Geany (e.g. colors, keyword list, etc as defined in filetype.lang) to do the syntax highlighting, but it does put the lexer framework in place, and such information can easily be obtained, maybe from SciTE or the language specification or any other text editor. If I'm right about this, it shouldn't be too hard to add a lot of new languages at once to Geany. Then again, I'm new to Geany's internals, so please correct me if I'm wrong.
Scintilla 1.75 also offers several other improvements. I myself am partial to the fact that it can render indentation guides over blank lines. Does it seem like a good idea to move to this newer version of Scintilla after the 0.13 release?