I think we're reaching a point this year, give or take, where developers who don't update their UI to be resizable, at the very least, will find less business and more and more complaints.
As a developer I know that a complete update of the UI stack is not an easy task.
OTOH as a user I just won't buy a plugin that doesn't have a resizable UI in 2020. The UI and UX are fundamental to a good software product. I won't spend any more money on mediocre products.
It's incomprehensible that even big companies like Izotope, Arturia, etc, are releasing products (Stutter Edit 2, Pigments 2) that do not work properly on hiDPI monitors. I know because I've experienced those first hand.
And then you have small companies like TAL, Kilohearts, U-He, FabFilter, etc, which do things right.