[jerf]

"try not to use markup on the JSON, because this would make it difficult for others to consume your website with JSON."

Since there is no standard for representing rich text in JSON, if you want rich text, this is simply an unavoidable problem. At least Markdown is semi-standard and people can get libraries for it. Embedded HTML would also work. Defining an ad-hoc rich text embedded would be worse.

[gpnt]

You are correct. Sometimes, some markup is inevitable. You can try to break down the information to render separately, but it is not always possible. So I think a little bit of markdown would be an acceptable compromise.