According to Alex_Sr's thread here (Statistics of user registrations on Bitcointalk 2017-2019), we are currently looking at around 20,000 new accounts per month, but we were over ten times as high during the height of the bull run.

It is impossible to know how many of those accounts would have had their first post deleted under this new system. There is no way we would ban these accounts for making one poor post, and so it is impossible to quantify how many would go on to make a second, third, fourth, tenth, twentieth, etc. post which would also need to be reviewed under such a system before they were "whitelisted". There is obviously also accounts which are created and do not post.

Given all these unknowns, we can't know for sure how many posts the mods are going to have to deal with. Given the small number of newbies who earn even a single merit, I suspect that the vast majority would be making at least 5 or so posts before they were either whitelisted or they gave up. I would take a wild guess at the mods having to deal with somewhere around 3,000 or so posts a day, which I think is pretty unfeasible. This number would increase massively if we see another spike in registrations during the next bull run.

Regardless, theymos has been pretty clear in the past about his reluctance to re-introduce newbie jail or any other kind of blanket restriction on newbies, and I tend to agree with that. A system like this is also going to turn away a great deal many of good and interested newbies, and that's the last thing we want for the future of the forum.

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.