I personally prefer not to use an initial ram disc, so moving all binaries into /usr is a plain *bad* idea. I do keep most binaries my separate, read only, /usr partition but I need the tools to mount it on the root filesystem.
Keeping at least some tools allows me to upgrade those tools without re-installing grub and running of out of space in /boot, which is also a separate partition, which I usually mount read only.
I would like to be able to mount / read only too but that is more difficult.