Hi,
I use the read-only mode a lot. I don't understand why it should be removed. If it is for the sake of clarity, I think you could add visible labels that say, for example: MD Editor, MD Viewer, Rich Editor. This would make it easy to see which mode you are in at any given time. In my opinion, if something is removed it should be the rich editor, because it has many limitations and sometimes alters the text written in MD. Joplin is a MD note software and I think it is not necessary to have a second (and problematic) WYSWYG editor.