High quality UX controls rarely are. I love slides.com and pay for the premium option to support the efforts. It’s awesome that they let you take a zip extract of the html/js version and run your whole presentation offline, which is handy at conferences. You can also export to PowerPoint and pdf too, which is was useful a few times.

TeXmacs will probably meet my needs then ... not as much sizzle and flash as reveal.js, but better WYSIWYG support for technical content.

For anyone still looking for an open source editor:

https://docs.deckdeckgo.com/

https://pencil.evolus.vn/

http://thomas.nadev.net/notes/2017-inkscape.html

https://github.com/rainwoodman/inkslides

https://sozi.baierouge.fr/

no, and neither i have found a similar layout editor that is open source.