I agree that adoption will likely be difficult. Basically the larger the engineering org the greater the benefit. If a company only has a few proposals a year then RFC Hub is mostly just friction.
I've worked at a few companies with thousands of engineers and where I've had to review hundreds of proposals. That's where the product really shines. Of course I do want it to be useful to smaller orgs as well. Adding Google auth should help reduce signup friction.
As another person on here put it, RFC Hub will benefit from automated importing of proposals. To be maximally beneficial all engineers at a company need to have an account and all RFCs need to be in RFC Hub. It almost requires a top down mandate which is bad. I do hope to make it incrementally beneficial for smaller teams.