I've described what intuition is, you haven't addressed it, familiarity with convention is not intuition, it's just knowledge. And given that convention is unintuitive (_ for underlining would be, and on typewriters underscores were also used to, you know, underscore text), that's a bad convention
Also, this /convention/ already exists and used, despite its low popularity (eg orgmode or Bear note app), so you're also literally wrong here
He said the convention that doesn't exist was -backslashes-.
Also, intuition is "understanding without conscious reasoning," so remembering a convention IMO counts.
Consider e.g. parental intuition of noticing subconsciously it's too quiet and immediately going to find out what the kids have done.
For UI, consider the floppy disk icon often used for 'save' - it's considered intuitive because the vast majority of users already recognise it without having to think about it, even if they've never had a system with a 3.5" drive themselves.
"Intuition is the ability to acquire knowledge, without recourse to conscious reasoning or needing an explanation" per wiki
The convention is the precise rule that _ is italics, so no, you aquire no knowledge, you need to already possess that knowledge and remember that precise rule.
On the other hand, if you know that _ is __underline__, - is --strikethrough--, then you can acquire knowledge (guess) that / is /italics/ because the principle is the same - formatting text follows symbol's shape (though it's not a perfect mach since / transforms text, not adds new symbols unlike _ or - ). But that's still intuition (* for bold would not fit here)
The other bad analogies don't help resolve it, so best stick to the topic
From my point of view, you acquire the knowledge that this system also follows the convention by guessing that it does and trying it (though I was quoting a dictionary rather than a wiki; I usually do for word definitions).
I appreciate that you don't find the analogies convincing, but they do express how I (and many others) see the situation, and declaring it a failure to stick to the topic because it doesn't fit how -you- see things is unconstructive at best.
Also, this /convention/ already exists and used, despite its low popularity (eg orgmode or Bear note app), so you're also literally wrong here