I believe the TiddlyWiki editing experience is its most significant area for improvement

To build on @CodaCoder’s customization suggestions:

I agree, this is tedious — but I think, at its heart, it’s an issue with the story river, not the editing mechanism. The first thing I do with any new wiki is always switching it to Zoomin storyview; I’d recommend the same (or other single-view alternatives — plus navigation tabs, if you want them) to all my fellow story river haters.

I recognize that you weren’t asking for recommendations and may not need them, but I’ll leave a few here anyway in case anyone with similar desires would like some currently-available options:

Not-quite-off-the-shelf enhancements for your editing experience
  • Navigation tabs solutions (generally work best with Zoomin):
    • BuggyJ’s StoryTopTabs
    • Ton Gerner’s Tiddlersbar
    • @Brian_Radspinner’s Be Rad edition (uses a non-standard layout)
    • Unfortunately, I find it rather difficult to find demos for specific plugins in the CPL, but I know I’ve seen more modern tabs-based layouts there, too.
  • “Live-edit” alternatives (other than WYSIWYG options, several of which have already been shared in this thread)
    • @twMat’s SideEditor (which can be popped out into an external window)
    • “Quick edit” tab in the sidebar: shared here by @diligent_path; @Mohammad’s Narenj; possibly others I don’t have to hand at the moment
    • IIRC @TW_Tones had a variation on the open-in-external-window button that opened an edit-mode window instead. I think he originally shared it in the Google Group, but perhaps he still has a version he could link.
    • Somewhat related: @Christian_Byron’s separate-window preview, and other expansions in the same thread
  • Tutorial: A basic alternative layout - also courtesy of @Brian_Radspinner; a good starting place for anyone who does want to build their own ideal layout, as @CodaCoder suggests.