If your infrastructure is complicated enough to make let's encrypt non viable then you're large enough that a certificate renewal period of a year isn't that on

If your infrastructure is complicated enough to make let's encrypt non viable then you're large enough that a certificate renewal period of a year isn't that onerous to begin with. If anything at that point having multi-year long renewal periods just leads to more of a headache when it inevitably gets forgotten about since it's such an infrequent task.