The PXE Client System Architecture Type “BC EFI (7)” from RFC 4578

With simple boolean options, I've done a grep in /proc/cmdline, which is very easy. For key-value options, the set trick seems handy, though I haven't tried it. Specific answers to your questions:

1) Yes, it sounds like this will work. I've done very similar things with kickstart and /proc/cmdline.

2) No, I don't believe there is any better way. The kernel exposes its command line options in /proc/cmdline, and kickstart doesn't provide any high-level mechanisms for dealing with kernel command line options.

3) Yes, this has been done before. Try it out, and come back if you can't make it work.

A few additional thoughts:

1) Don't put a comma between the command-line options (just separate them with spaces).

2) With pxelinux, it can be helpful to use an append line. For example:

append initrd=f16-x86_64/initrd.img ks=nfs:server.example.com:/path/to/f16.ks mycustomflag mykey=myval

3) Network settings (like the hostname example you gave) are often better served by DHCP.

From what I gather in your statements, you have two disks with the following (or similar) disk layout:

sda: GPT
  sda1: Linux MD RAID member
  sda2: Swap
  sda3: BTRFS pool member (RAID 1 allocation policy)

sdb: GPT
  sda1: Linux MD RAID member
  sda2: Swap
  sda3: BTRFS pool member (RAID 1 allocation policy)

md0: ESP (~100mb? VFAT) mounted at /boot/efi (RAID 1 allocation policy)

BTRFS pool: 
  root subvol (mounted at /)
  home subvol (mounted at /home)
  et cetera ad nauseam.

This is exactly what you want in almost all cases, and if your configuration doesn't reflect this you'll probably want to make it reflect this.

The Linux MD volume in this case is a RAID 1 between sda1 and sdb1. Don't mess with sd[a,b]1 directly, and only ever mount the MD volume created from them (usually /dev/md0 or /dev/md/0 unless you've felt the need to give it a special name during creation). You absolutely must use RAID1 for the ESP volume, since the motherboard firmware expects to find that data intact on any single disk at boot time.

The swap partitions will naturally stripe, but a failure of one will not crash your system in almost all cases. Don't use MD for swap unless you have a good reason, as the pager is very smart.

The BTRFS pool will scan automatically, so it's best to specify this volume by UUID when adding entries for it in the /etc/fstab file.

GRUB2 can boot from any BTRFS RAID level. Just make sure that the "stage 1" loader is installed to both of the partition tables (sda, sdb). This is done when invoking grub-install /dev/sda (may be slightly different depending on distribution).