Yes, full support for Markdown (edit and display mode) on MAC client beta 1 (released yesterday), but read-only on other platforms right now (they said they are working hard to bring edit mode to every platform).
They add another standalone button in side bar under the present “huge” New Note button. This will create a special note called "Markdown Note", which can not switch to old type Evernote note.
I think this solution is not ideal and necessary for Evernote, because it's basically what Marxico can do right now. I wish Evernote original editor would evolve into a totally different, full-function tool for us, not this simple combination of two products.
The best solution I can figure out is "block", like Notion.so (unfortunately, its UI is not best for personal note taking). Web clip note or paragraphs would be treated as "HTML" block, and our own notes would be "Markdown". This different type blocks can coexist in one note, not isolated notes, like what Chinese Evernote "YinXiang BiJi" is doing now. This would be a solution for conflicts between HTML code and Markdown syntax.
I think EN team will not do that. They just want to keep the original editor simple and let third-party extensions do the other things. Partly, I agree with this thinking. However, the lack of “quote” and "code indentation and highlight" features really makes me feel the present editor is like a toy.