/ is too commonly used, such as when making a list of replacements/alternatives/synonyms. It works fine when it's just the text as written, but if it was parsing and turned that list to replacementsalternativessynonyms, it would only be getting in the way.

True.

Perhaps //italic text// would be acceptable.

// is common in URIs.

You shouldn't parse '/' in foo/bar/baz or in foo / bar / baz.

If people want to make foo or foo bar italic, they write /foo/ and /foo bar/.