I'm building a Gsheet addon that really solves a huge problem. However I'm skeptical about the scalability of the project.. anyone running a Gsget addon SaaS with more than 10k MRR?
I may help you but what problem?
I definitely should not give any advice here since I am not familiar with Google Sheet addons. But I think that crucial part is, as you say, that it solves a huge problem and I really don't see a reason why it should not be scalable. I believe you can scale everything once you know that you solve a big problem and you know/have people who have this problem.