How does that perform when the entire 12MB file is a single line?

Before you say it's unrealistic; sure, it's not a normal use case for code, but I frequently find myself wanting to open a huge JSON file, for example, just to perform a search/replace, or a minor edit, or copy some fragment, or just look at its contents. Pretty-printing first, or doing the change with a specialized tool like jq, is also something I do, but being able to just load the file into a text editor is often more convenient.

In my experience, editors tend to break down on edge cases like these. Editors (e.g. Jetbrains) often turn off syntax highlighting and/or edit capabilities on large files, not to mention put an upper limit on the number of cursors.