I honestly think you are looking for something else here. Bear uses markdown and so does its users. MD has a strict set of rules but most of all it has a "philosophy" which separates content from its representation. What you are proposing is a Rich Text editor and there are plenty alternatives on the App Store.
h2 Next, the annoyance
Yes, I agree headers can be improved, but we can't avoid both h1/h2 and #/## we had to choose between one of those.
I realize that this means that text would reflow as you move your insertion point around. That's fine - editing is a different modal activity from viewing/proofing, and I don't think that this would be disruptive.
I disagree: If you have to pass from view to edit mode 20 times a day and the text move is a deal-breaking experience.
Thanks for the response, Danilo. Yeah, I understand about Bear's philosophy, and I wasn't writing my suggestions in anger, but rather as constructive feedback. I think that you have the ability to be "not just a Markdown editor" and I described a couple of ways you might be able to do go in that direction (and keep me and people like me as customers in the process). Of course, you and your team need to do what you feel is right for the product.