You can ditch the initrd if you compile in the kernel the drivers you need to boot the system, as a minimal example SATA/SCSI, EXT4/JFS, that usually are compiled as kernel modules.
It never crossed my mind that LVM and similar needs utilities to access the filesystem and to be honest, I thought initrd/initramfs contained only kernel modules, not executables and scripts... ^__^;
Build a kernel with the most common hardware built into it, and use that to bootstrap. No need for messy things like balled up temporary rootfs in a ram drive.
Initrd/initramfs have become an excuse for piling on complexities that frankly should be added by the sysadmin after initial install.
It's not very common to need kernel modules (drivers) on initrd on typical hardware.
You can of course accomplish similar things by just recompiling the kernel (which Slackware makes very easy to do), but if you still need to use 'mkinitrd' anyway (perhaps because you're using LVM or softraid or LUKS), it's often more convenient to just throw in the modules you need while you're at it.