In reply to twsjonathan.

I think they should work through it in consideration of their customers and reputation. Maybe hire somebody from the WP theme review team as a consultant to come up with some specs. Follow this at the very least: https://make.wordpress.org/themes/guidelines/guidelines-plugin-territory/

Give plugins not using CPTs, shortcodes, etc. a special "Avoids Lock-in" badge and let buyers search for those themes. I think something like this could educate users and encourage authors to make better products in the future (they'll have to if buyers start seeking out these types of themes).

I thought about a year ago Envato was getting ready to put measures in place to require new submissions not to use CPTs in themes with a plan to eventually require old themes to be updated. Do you remember that? I haven't been active on ThemeForest for a while. What came of that? It sounded difficult from a short-term business perspective but wonderful in the overall scheme of things.