I don’t see why I would switch from iA Writer, which is already a refined Markdown editor (and is cross platform).

What did I miss on the landing page?

similar to Typora but doesn't seem to have Themes.

It's a beta from the team that built Bear (Bear.app), which has themes. Would assume they're coming later.

Which also means they’ll ask a subscription to use a text editor.

There are discussions on the forums on this. Nothing is decided yet.