>... especially with cross-group transactions (added last year)...

Thanks for mentioning this: I didn't know they had added this feature; that definitely makes some of the data modeling problems easier. Without this, I found it often led to situations where you had to make horribly painful decisions that affected both functionality and scalability very early on in your project lest you end up with tons of data that you now have to programmatically and mostly manually migrate (which is why, to me, I keep being surprised that you keep mentioning ops challenges for normal databases: with the ability to do global schema and index changes concurrently and safely inside of transactions, I found the amount of time and thought I need to put into managing something like PostgreSQL a fraction of most alternatives that supposedly scale better).