Hi,
Page builders were always popular here on ThemeForest! Today, I’m here to introduce Dasht: An advanced drag and drop site builder for HTML templates.
It allows buyers to build and edit pages without any coding. Just like Elementor for WordPress themes.
Take a look here:
https://dasht.io
or watch a demo video (pre-made template):
Let me know if you have any questions. I’m excited to know what you think about it? 
We want to provide this service to theme authors and looking for a few volunteers! (It is currently free and we’ll do all the hard works)
You’re a bit late for this one as HTML sales on Envato is not really good anymore as before and most of the users who’s buying the HTML templates are already good with HTML/CSS
@ki-themes is right - there’s been a few really intuitive builders like this over the years, but even the best from established authors have not sold particularly high volumes.
Aside from the often bloated html/css files that these often unavoidably produce (which can frustrate more experienced buyers), it is serving a bit of a void area where less experienced buyers will still default to WP themes given the extended simplicity that full CMS offers