Fund Prosemirror if you have ever been frustrated by a WYSIWYG editor. Not because Prosemirror will be frustration free but because more effort in this area is necessary to get there. -> insert link to any Contenteditable WYSIWYG editor

Fund Prosemirror because you think collaborative rich text editing should not be a technology reserved only for web giants to have and acquire. Firebase/Firepad(acquired), Hackpad(acquired), Appjet/Etherpad(acquired), Wikidocs(acquired)...

Fund Prosemirror because Marijn Haverbeke has a good track record with Code Mirror. https://codemirror.net/

Fund it because open source shouldn't only be about free as in beer. http://coderanger.net/funding-foss/

Fund it because it is an impressive piece of work in its own right and current state. http://prosemirror.net/demo_collab.html#edit-Example

Fund it because in Marijn's altruistic intentions -- its already on github https://github.com/ProseMirror/prosemirror to look at, he's asking for only a very small amount of compensation for a ton of work, and he's written incredible blog posts educating everyone. http://marijnhaverbeke.nl/blog/collaborative-editing.html

Fund it if only because you have faith in humanity.