What I would love to see in the Debian ecosystem is a "Slowroll" release, similar to OpenSuse's upcoming "Slowroll" option. Maybe take Sid and make include any Sid packages that have been in it and stable for at least 2 weeks, and release an update every 30 days or so. Do some additional testing, backport any critical security fixes... sounds like a lot of work but it would be a valuable option.
That is mostly what testing does, modulo the exact numbers/durations involved.
One reason people don't do snapshot-releases of testing is that such releases wouldn't get security support. And security support shouldn't wait 30 days.
Which is why I explicitly mentioned security stuff being backported. Maybe it wasn't clear enough, but yes, I agree that security updates need to be released faster in many cases, and need a special handeling. The amount of work involved in handeling security patches is probably why it hasn't happened yet.
