I expect we're in your target demographic, small team using Next.js and Supabase with a lot of ambition and not enough time in the day :)
Stack Auth is one of those things I didn't quite realize I might want – we're using Supabase Auth at the moment during our EAP, with Nango as an OAuth proxy, and I've been hesitant to build out organizations without a good reference implementation – we've rolled it ourselves before and never been really satisfied with the results. At the moment we're rolling a deployment-per-org, which is ok for small teams, if a little cumbersome to manage, but we'll need a solution for larger companies. I've had supabase_rbac[1] in the back of my mind for this.
Stack Auth seems like it could solve a few of these, but do you see yourselves proxying APIs for OAuth, or will you leave that to other service providers?