This is very similar to the shadow ban system that Hilariousandco has suggested a few times in the past. In theory its a great idea which would prevent spam being seen to the public eye, however whether we have enough resources to handle that amount of posts a day would be debatable. Despite reports not coming in as thick, and fast as a few months ago I would still say that amount of posts could be a little bit hard to deal with. We would likely need a few more moderators in each of the sections. There are still global moderators which have a dedicated section which could probably be optimized by adding a few more moderators to help them out, but only they really know how much additional help is needed.
I for one don't really like imposing restrictions on the majority just because of the minority is causing a few issues. These bot attacks are somewhat quickly dealt with as a community effort, and they aren't as popular as you might think at least to the scale of yesterday. I would have to agree with o_e_l_e_o that imposing to much restrictions is not beneficial to the forum as a whole.
Perhaps a better option to have dealt with the recent spam attack would be to give global mods or a slightly larger subset of the mods the ability to auto-ban all accounts posting a specific phrase or link.
I think the recent bot attack was pretty well dealt with, and a big part of that was down to Mitchell's bot. Reports have died down in recent months across the boards I would say, at least in the sections I moderate, and newbie reports have significantly died down. Although, there are still a few prominent users who are reporting fairly regular.