> on i386 the userland/kernel address space split is configurable
If you're going to modify the kernel, might as well just install x86_64 instead.
> an area where amd64 is worse is security due to the lack of segmentation, the baby went with the bathwater unfortunately
Bah! Linux never bother with much of the segmentation crap that i386 uses to begin with. Sure, it separates userspace from kernel space, but it does nothing to protect one task from another. Page tables are used for that purpose.
Show me one security errata that was the result of removing segmentation from x86. And I mean for Linux.