As to the hidden devices issue, I honestly don't think I've ever even noticed it personally. If I'm cleaning up a machine from a virus infection I'd go straight to the underlying registry entries rather than mess around trying to disable them in Device Manager (something it's much easier for them to counter by re-enabling them before you've done anything else). The inclusion of an anti-malware engine in Windows 8 should also hopefully mean that less people actually get infected from day one, or at least have it auto-cleaned without messing around doing it manually.
I sort of agree with your other points, I included them for completeness, but the non-pnp devices are very useful. Not only for malware, but to see what applications in general load up. I've just noticed that VMWare Player whopped up five device drivers here. Useful info.
And as I said it's not only for malware, CD-emulation software is notorious for messing up stuff, this can be usually solved by deactiving its non-pnp driver.
I see no reason why this had to be removed. It also makes developing certain applications not exactly easier, like AV.
I am asking you: What good is achieved by removing this feature?