Problem with nostr clients using markdown for kind 1 events is that it can look quite ugly in clients that don't support it. Other clients automatically detect hyperlinks, images, etc. and render them in their own way.

Perhaps there should be some way to signal what kind of formatting is required, a 'formatting' tag for example.

In NIP01 it says that kind 1 events is only for plain text, whether markdown qualifies is debatable, I guess.