Rather than maintain an in-house editor for Notes, incorporate the TinyMCE ( https://www.tinymce.com/) editor into the Evernote Web Client
TinyMCE is a fully featured, embedded HTML editor, that could provide all the edit feature typically available in many web-based application and provide a more consistent and feature-rich editing environment across all supported platforms
ENML may need to be extended to allow support for the additional feature of HTML5, or conversely the editor could be "cut back" to only support the elements currently available in ENML