The BookStack has an impressive use of draw.io in their wysiwyg editor. There is often use for drawings to show what you mean in a written topic. Please try their demo (bookstack) to be inspired!
Ability to paste images into MD editor
Images should be pasteable via clipboard ctrl+V as a shortcut, similar to how Github's MD editor works. This would be a gigantic time saver.
Handle multiple users editing the same page simultaneously
Prevent overwrite when more than one user are editing the same page at the same time. Offer merge / diff view?
Talk / Discussion feature per page
Ability to leave comments and discuss on pages (like MediaWiki).
Have a template or transclusion function, just like in MediaWiki(https://www.mediawiki.org/wiki/Help:Templates), which would give people the ability to create infoboxes or other types of templates that are used on many other wikis.
Have the option to add a company branding to the interface as well as some kind of copyrighted footer. This would help in case of printing pages in pdf.
Support AsciiDoc format
Many recent projects are using AsciiDoc to manage documentation and deliver diffent document types (html, pdf, ppt ...). It would be great to add AsciiDoc support to that files. There are already available lib for node (https://github.com/asciidoctor/asciidoctor.js) that could be integrated.
Collapse items of menu
To improve navigation on index menu of each part of wiki. The introduction of this system navigation permit a best construction and reading capability.
When opening a page from the navigation side window (/all), the navigation should stay visible on the side.