I will say that forward slashes are still more common in regular english text even among non-programmers than underscores. For example, listing options a/b/c.
I don’t really think of Notion as “markdown” but I suppose you’re right since we support a bunch of markdown conventions. Some things are different though like `> ` is a toggle block, and `” ` a quote block. Unfortunately we already abuse / for a command menu, which is by far my least favorite feature. I want to make a setting to disable it but it goes against our anti-settings philosophy.
Using slashes for a short/small/abbreviated list is relatively common. For example, the top post on the hiring thread right now is for a "Full-stack/frontend/product engineer". There's another one describing a "M/W/Th" hybrid schedule.
Not even common including file paths, unless you mean directory paths. Even then, only necessary if you really want to unambiguously indicate a directory in the path itself.
no, but most people definitely use links in their texts and they have the same problem. / is also regularly used for fractions or/and in a situation where you could use two words