Make region-collapsing limit depth, to avoid horribly sluggish document editing
When the document you're editing is BIG, but not big enough to cross the "too big for collapsible-region support" threshold, text editing becomes SUPER sluggish. Like, typing or backspacing multiple characters takes over a second for each character to appear or disappear. And ironically, the bigger the document is, the MORE likely region-collapsing is to be USEFUL!
So here's my idea: LIMIT THE DEPTH. Instead of just "shutting it off completely" when the document is larger than a certain threshold, only allow ONE level of region collapsing (indentation 4) for huge documents. For very large documents, only allow TWO levels of region collapsing (indentation 4, 8). For big documents, THREE levels of region collapsing (indentation 4, 8, 12). For small documents, go crazy and allow infinite levels of region collapsing (indentation 4, 8, 12, 16, 20, ...).
Yeah, I know, ideas are easy, implementation is hard. You're probably using some third-party library for the visual editor and the section-collapsing feature probably didn't anticipate this manner of limiting itself. Oh well, something to consider anyway, because editing large documents really sucks the way it is now, but region collapsing at the outer levels is too useful to just blanket-disable entirely (assuming there even IS a way to blanket-disable it)