Indent for code blocks is a non-starter. Can't paste easily, very annoying to type in a web form. Triple backticks is the right thing.
Triple backticks also let you specify the syntax very conveniently.
Add to that using -> to designate a link with a numbered URL for the actual href (numbered hrefs are already in Markdown), and also needing to indent list items... this is a solution in search of a problem.
I wish HN supported triple backticks.
That said, I think it would be better if the closing delimiter was different from the opening one. Yesterday I had an LLM output text where it forgot one of the delimiters, causing all text inside code blocks to actually be outside and vice-versa.