A problem would be the security updates. You can't really spend even 'more' people on security updates for a rolling release. The frequency of updates would be too high for this to work.
This is also the reason for only stable (and olstable?) getting security updates. The thing is that if you want to support something, you'll need to scope it. You can't support just any random thing, you'd need an army of maintainers just to do that. So you make a 'release' where that specific version has people watching over it and making sure things are safe and working. Even that process is hard enough as-is.
While it would certainly be nice to have a rolling release, or 'really fast' release, it can only be done if more hours/people/donations are available to fuel it.
Having security support for renamed testing would be more work than now but not the kind of work security support for stable is. Security support for stable involves backporting fixes. For a rolling release it would mean expedited pushes of upstream versions with security fixes in them.
This is also the reason for only stable (and olstable?) getting security updates. The thing is that if you want to support something, you'll need to scope it. You can't support just any random thing, you'd need an army of maintainers just to do that. So you make a 'release' where that specific version has people watching over it and making sure things are safe and working. Even that process is hard enough as-is.
While it would certainly be nice to have a rolling release, or 'really fast' release, it can only be done if more hours/people/donations are available to fuel it.