Nice list.  I'd add

Better support for read-only (or read-mostly) boot disks; right now;
you have to play funky games with mfs/tmpfs file systems to hold
unpacked copies of /etc and /var.

Maintenance -- I have a 3.99.7 box that I wouldn't mind upgrading to
4.0, but it's too painful to figure out exactly what to replace, given
the highly customized setup.