Earlier quoted context omitted.
IMO the biggest omission in Unicode are game controller button and keyboard emojis, as very frequently arise in game tutorials.
Most games aren't shipping with full-fat unicode support or typefaces that could display those icons, though. Plus it'd start to break down with controllers that aren't simple A/B/X/Y.
There is a combining character that, by its description, sounds like it should be implemented to do the desired thing (U+20DD Combining Enclosing Circle), but my fonts don't render it very well when I stuff geometric characters matching the PlayStation buttons into it.
Without spaces: △⃝□⃝×⃝○⃝
With two spaces between each one so you can see how "enclosing" is getting interpreted: △⃝ □⃝ ×⃝ ○⃝
For the Markdown renderer I'm working on to replace WordPress for my blog, I resorted to shortcodes which resolve to CSS styling the `` tag with `title` attributes to clarify and the occasional bit of inline SVG for things where I didn't want to specify a fixed font to get sufficient consistency, like PlayStation button glyphs.
(In all fairness, it's a nerd-snipe made based on the idea that I'll be more willing to blog about things I have nice tools for. I don't currently typeset button presses in any form.)