My concern isn't for DR itself. Like I said, it would be terrific for that since it would simplify protection. My concern is for testing DR without affecting production. If you're willing to do a live failover of production then this is a great solution. However, I don't have any customers who would be willing to take that risk. Testing SharePoint DR usually involves a temporary (or even permanent) duplication of the environment, either as a cold/warm/hot environment or via a replication technology like Azure Site Recovery (which is what we're looking to use with my current customer). These DR tests would need a copy of the SQL instances as well to operate, and it looks like this would be a big challenge when using SQL Managed Instances. But again, maybe not. I'm probably just not seeing something obvious.