I've attended a few Unitarian Universalist services, and they're very open to "non-believers", as well as pretty much any type of personal belief. They seemed to be much more interested in community and rite than to forcing dogma. Still, while they were certainly a friendly and pleasant group of people, I found it all a bit too fuzzy with objective truth to be my cup if tea. I don't have anything like Sunday Assembly in my area, and occasionally thought of trying to start some kind of weekly humanist gathering. Rather than the UU message that "any belief is welcome", I wanted to convey more of a "everyone is welcome, personal religious beliefs aside" message. Where we could just work on humanistic goals together.
This is very interesting to me. I am just "Saturday browsing" but plan to try to read what I can about your community. My first impression is surprise that the group was trying to raise venture capital :) I will find out more as I read i guess.
Take the best bits of religion, including purpose, structure, community, and tradition, but make it available for non-believers.
We even got so far as making the interview stage of Y Combinator:
https://benrmatthews.com/meeting-heroes-y-combinator-intervi...
During the interview, Sanderson (Sunday Assembly co-founder) had a brilliant back and forth with Sam Altman, but ultimately the idea didn’t stand.
I still think the ethos of Sunday Assembly has merit.