No way. Every time I've worked with an organization with three years expiry it's guaranteed they have no idea, after three years how to even renew the cert. They are effectively longer in many cases than the hiring cycle and for larger organizations can be a complete nightmare. No one wants to invest in time in automation, training, tracking, etc., because it's so far down the road. The 90 day model makes much more sense because it requires automation. In terms of the ACME endpoints being down, I'm not going to say that won't happen but renewal starts 30 days before the cert expires and if Let's Encrypt's ACME endpoints are down for 30 days or longer there's a good chance we are all dealing with something far more dire than cert renewal at that point.