John Yeung:
I'm slightly surprised that you would prefer Geany over a whole slew of editors designed for writers. Not that it couldn't happen. Are you aware of having an unusual workflow, for a writer? What is it about Geany that makes you prefer it over a writer's editor? (Genuinely curious, plus wondering if it wouldn't make sense to see if you can't get your desired features into one of those other editors, rather than make Geany look like those other editors.)
I don't think there are writer's editors. These are just marketing labels. Or, from my experience, if there is one, than it is Microsoft Word by far.
I simply like line numbers. And having the ability to use versioning from the editor. Or having two files side by side. Or having the same file open and ready in two places on the same screen. Or a clean list of open documents to the right side. Powerful find and replace. The ability to insert the date formated as I want. Case toggle. Minimise to Notifications. Bookmarks, although I would have liked something closer to Word with links. Colorschemes.
I would have liked folding. But I am not aware of any text editor smart enough to do markdown folding. And having the ability to edit somewhere between half screen and the end of the second third.
Geany is quite low on resources. Surprisingly for its complexity. Meaning it loads fast and it's quite uninpressed by other apps eating all the CPU. And while there are even lighter editors, they lack most of the above.