I think it’s pretty funny that we’re now arguing about going from tests-passed to beta, since back in the day the argument was about going from beta to stable 
I guess that changed at some point.
I’m still on the self-hoster’s side of the argument, but Discourse as a project is clearly in a tough predicament on this one.
In the WordPress community, self-hosters default to stable while wordpress.com is on the equivalent of tests-passed. There’s no doubt this has been a huge contributor to WP’s developer ecosystem, since developers can take aim at a stable target for about 3-5 months at a time. Say what you will about WP’s wild assortment of plugins; the level of developer engagement they have is unprecedented.
The price they pay for this is all the work that backporting security fixes entails. I’m not sure how much work it would take to backport only critical security releases to the Discourse stable branch, but I’m sure it’s not trivial. We need to get bigger before we can feasibly absorb that cost on behalf of the community.