I have just checked the page of iA writer.
No justfied text, no paragraph margins? In 2017? This would have appeared as severe in 1997.
(Also, a sinister communication style.)
Editing markdown and then previewing is a more complex operation then directly inserting richness in the text, a feature that we have been using for decades (editing the source remains important for specialists, but not with markdown). And desktop devices were not more powerful back than nowadays mobile devices.
All Word Processors have immersive mode*. Kingsoft has a menu bar that hides or shows the toolbar by subsection. In "web layout" mode, the "virtual sheets" disappear. In editing mode, all you see apart from the text are that simple bar and the text. And in reading mode, you go fullscreen: the text area goes from corner to corner.
Kingsoft 5.12 is found at
http://m.apkhere.com/app/cn.wps.moffice_eng
, almost last link, after the developers broke the link at their site,
the latest version of the reforned product (WPS) again on that page or on Google Play.
*I realize while writing that somebody can now try to sell software as "immersive" after a most mainstream producer (reseller, some say, but I don't know) broke traditional interfaces ten years ago cluttering the screen with huge, messy controls. Their impact is widespread if you count diffusion, but limited as most did not follow their dubious idea.