Pretty amazing how virtualization has come to the point that we even need to virtualize our reliance on cloud vendors across multiple vendors to ensure realiability
I'll say, I've only really done multi-cloud for cases where I liked different products on different clouds -- the main app and data on AWS, but using Google's data stack (BigQuery >> Redshift imho).
In terms of reliability, I think the first step is multi-region -- being able to failover to another region should your primary region have major failage. But assuming you can do that, doing multi-cloud for the same thing shouldn't be so hard provided you have some sort of common open source runtime to run on both platforms.
