Just adding some things. I'm not a theme developer, so this might be obvious to those who do.
I've started to put together a Hugo version of the Wordpress "theme unit tests," which are a variety of basic and edge-case pieces of content meant to test the versatility of a theme.
Thinking out loud here, but perhaps, with that there could be a repo of a sample site (I've already started one for my own work, and note there's a basic example for theme display), and with that Hugo instance, there could be a checklist that shows:
1) Community Review, using the unit test content and a general review of the code with standards like
- archetypes in place
- more stuff here
2) Run a Hugo benchmark command for build-performance.
3) External tests: webpagetest.org, Lighthouse, webdevchecklist, HTML proofer.
*Note: as a user of these tests, I know they can be maddening. I think some minimum standard could be identified as acceptable.
Not saying that every theme should go through this, but, setting something like this up and identifying/highlighting themes that meet these "standards" would be a good incentive to theme developers.