i've said it before, but is anti-cheat mechanisms needed on consoles? If not, (presumambly due to their locked down nature), what's the problem with having a locked down mode (trusted secure boot path that doesn't allow other programs to run, ala "the xbox mode" that microsoft has started to implement), that is similar to a console.

This seems much more doable today than in the past as machines boot in moments. Switching from secure "xbox mode" to free form PC mode, would be barely a bump.

Now, I see one major difference, heterogenous vs homogenous hardware (and the associated drivers that come with that). In the xbox world, one is dealing with a very specific hardware platform and a single set of drivers. In the PC world (even in a trusted secure boot path), one is dealing with lots of different hardware and drivers that can all have their exploits. If users are more easily able to modify their PCs and set of drivers one, I'd imagine serious cheaters would gravitate to combinations they know they can exploit to break the secure/trusted boot boundary.

I wonder if there are other problems.

Not sure if they are considered anti-cheats, but there are some measures to detect usage of input devices like XIM that allow keyboard and mouse inputs which allow for superior aim over controllers.

Well it's definitely not game developer written kernel anti-cheat on consoles.