I'm still largely undecided about what to do with text formatting. The theme isn't a barrier to that, remember that it's just the theme for *this* forum. Other website may be using this software with a different theme; so I will add bold and italic markup, they will just appear visually different on this site (bold is white and italic could be a different colour).
I use the tildes just because it looks nice and clear and it's immediately apparent what it is (rather than --- which is understood as a paragraph break, like `<hr />`).
I like syntax to be lightweight and plain-text readable, so some of the ideas in ReMarkable are a good starting place, like the *bold* and _italic_ formats.
Also, remember that we're looking for simplicity and a lack of superfluousness. For example, there will never be a way to make hyperlinks without the URL being visible. This just helps spam and people who wish to abuse the site. It does absolutely no harm to me or you by having hyperlink URLs always visible.