Longer-term, we need to move to browser-native GUI, yep. The nice bits though - the entire document loading, rendering & editing works in the browser now.
We already use cairo/freetype/skia to do essentially all the document rendering in software (not for the Qt prototype though), so that's not a big leap to get that blitted out.
Incrementally then using more of html canvas to speed things up might be next.
Most of the work is going to be having the GUI (toolbar/notebook bar, menues, sidebar, dialogs) browser-native of course.
Can you elaborate?