Yes! We're definitely talking about the same thing here! Definitely not thinking of consistent writes to both views.

Now that you said this about watermarks, I realize that this is definitely the same idea as streaming systems like flink (which is where I'm familiar with watermarks from), but my use cases are smaller data and I'm looking for lower latency than distributed systems like that. I'm interested in delays that are on the order of double to triple digit milliseconds, rather than 15 minutes. (But also not microseconds.)

I definitely agree that it's difficult to justify building this, which is why I keep looking for a system that already exists :)