1) It is in fact possible but as noted previously, most people still wouldn't feel comfortable running their core business long-term on this kind of tool. However, no one worries about running their business on AWS and in fact our infrastructure is on top of them (like Heroku). So we need to grow a bit more before people are OK with that :)
2) Retool is tailored at internal tools, so you can't quite customize the UX as you'd want for something that is touching end users. Besides, it's quite expensive for the MVP use case because they price per user (we don't, our pricing page is coming soon).
I would prefer to use this sort of things for longer term but non-core functions (e.g. back office).
I agree with OP that it's a weird use case, as a focus on short-term MVP may limit user retention if you actually succeed (or is the idea that people will accidentally start to use it long term?).
2) Retool is tailored at internal tools, so you can't quite customize the UX as you'd want for something that is touching end users. Besides, it's quite expensive for the MVP use case because they price per user (we don't, our pricing page is coming soon).