When I went to preview the article, the sidebar was gone on desktop in Firefox 50.1.0 on Windows 7. Is that deliberate? I felt disoriented without the expected sidebar--not that I was planning to use it, but it wasn't a faithful representation of the end-effect (which I would guess isn't as big an issue as the topic below w.r.t. differences in parsers).
Topic on 2017 wikitext editor/Feedback
Preview "oddity" w.r.t. sidebar
Team is considering options. Please suggest ideas!
True, it's a bit different from the regular desktop reading experience, though it's a pretty faithful view of what readers see on mobile (with some notable exceptions like infoboxes), of course.
We're still thinking about how we could make preview mode more useful — one possibility is to replace the editing surface with the preview, though that might also be confusing. I'd love to talk about any ideas you might have to make it more useful.
I'm just not sure it makes a lot of sense in this context--as part of the introduction of a new editor. If I were looking at such a thing from a scope perspective, that change would feel like scope creep, or like someone was trying to sneak in this change. You might face resistance to it which is unneeded in this context (VE/Parsoid/VE-inspired WT editor doesn't need help w.r.t. resistance).
I'm not entirely sure what you mean when you say "replace the editing surface with the preview".
Mostly, the biggest thing I'd appreciate from a preview mode is not having it; a side-by-side render of wikitext and preview, or perhaps, being able to side-by-side jump from editing in the wikitext form to editing in the VisualEditor. I can skip the clumsy UX step of "does this look the way I want?" and go straight to "finis". (A mode which might only work well at resolutions above 1400px or so given the penchant for floating boxes of various sorts in wiki content.) I'm fairly certain that such a thing would need to be looked at for performance issues, naturally.
The preview is currently shown in a dialog (which we make fullscreen to be as wide as possible). "replace the editing surface with the preview" would mean replacing the area where you are currently editing the wikitext.
Like Flow? That doesn't seem like a horrid option, so long as there is a sensible icon to switch back (and I was meandering yesterday and know there's a task for picking a new icon).
Yes, though we'd want to avoid confusion between editable-visual-surface and read-only-visual-surface. We'll play with some design options to see if we can come up with something along these lines.