Pretty nifty overall, and look forward to seeing where all this goes. I've done some similar musings for my own AU. Really like the square model being used, something that has seen a lot use at my table (mainly because I have 4 players so it's easy to do)
On the above I quoted, I could be wrong but I seem to recall that various mechs would be selected as the new standard for the FedCom with the goal of making something look homogeneous. I think it was in a TRO but could be wrong. Obviously never happened, but maybe the intent was there. Want to say it referenced designs like the Valkyrie and Wolfhound, Victor and Zeus, etc. Basically designs they built and wanted to improve manufacturing more of.
Maybe in the Project Phoenix TRO? I know if you look at the RATs, it never really happened to the level I envision. LogCom wants five types per weight class period, FedCom TRADOC equivalent says not doing because a Command's doctrine might not be compatible with those machines, and High Command says LogCom isn't going to screw over local manufacturers.
I haven't counted the chassis and variants, and won't right now because I'm due to punch back into work, but I'll do so once I get home. I
think it'll be under 20 unique mechs and certainly under 30.
EDIT: So, here we are.
RCT Command Battalion: Rifleman 8D, Longbow 12R, Stealth 2D, Night Hawk 2Q, Hollander F3
Davion Light Guards: Uziel 3S and 4S (MWO 3P), Crab 29 (non-cannon), Hellspawn 7D, Legionnaire 2XA
Davion Heavy + Numbered Guards: Marauder 7D, Warhammer 9D, Rakshasa 1A and 3A (non-cannon), Rifleman 8D
Davion Assault Guards: Nightstar 9J, Sagittaire 8R, Longbow 12R and 8V, Templar 3D (non-omni/non-cannon)
Kettering Lancers (reflagged Crucis Lancers): Warhammer 8D, Thanatos 4D (non-cannon), Avatar 2D (non-omni/non-cannon), Rakshasa 3A
Messengers of Shiva: Warhammer 8D, Falconer 8R, Rakshasa 1A and 3A, Rifleman 8D
Robinson Chevaliers: Warhammer 8D, Falconer 8R, Argus 2D, Rifleman 8R, Rakshasa 3A
Tancredi Loyalists: Warhammer 8D, Falconer 8R, Argus 2D, Rifleman 8D, Rakshasa 3A
Kittery Borderers: Warhammer 8D, Falconer 8R, Rakshasa 1A and 3A, Rifleman 8D
Aragon Borderers: Cataphract 3D, Falconer 8R, Rakshasa 1A and 3A, Rifleman 8D
FSAC: Falconer 8R, Warhammer 9D, Hellspawn 7D, Uziel 4S, Legionnaire 2XA
Arcadian Cuirassiers: Cataphract 3D, Falconer 8R, Rakshasa 1A and 3A, Rifleman 8D
Argyle Lancers: Falconer 8R, Uziel 3S and 4S, Hellspawn 7D, Legionnaire 2XA
Deneb Light Cavalry: Bushwacker S2, Uziel 3S and 4S, Hellspawn 7D, Legionnaire 2XA
Dragonlords: Nightstar 9J, Sagittaire 8R, Longbow 12R and 8V, Templar 3D
Kestrel Grenadiers: Nightstar 9J, Sagittaire 8R, Longbow 12R and 8V, Templar 3D
New Ivaarsen Chasseurs: Falconer 8R, Uziel 3S and 4S, Hellspawn 7D, Legionnaire 2XA
Kearney Highlanders/Northwind Hussars/MacLeod's Regiment/Marion's Highlanders/Stuart's Highlanders: Falconer 8R, Crab 29, Hellspawn 7D, Uziel 4S, Legionnaire 2XA
Northwind Fusiliers/Northwind Guards/Stirling's Fusiliers: King Crab 001, Highlander 735 (non-cannon), Longbow 12R and 8V, Templar 3D
FedSuns Unique Chassis: 22 (25 if you include variants)
Royal Guards: Highlander 735, Zeus 9S, Salamander 5S, Emperor 6S, Thunder Hawk 7KMA, Dragon Fire 3F, Maelstrom 5S, Archer 6S, Rifleman 8S (non-cannon, 8D with LBX), Crusader 6S, Bushwacker S2 and S3 (cannon X2), Uziel 3S and 5S (non-cannon)
Arcturan Guards: Marauder 9S, Warhammer 9D, Archer 6S, Rifleman 8S, Crusader 6S
Donegal Guards: Fafnir 5, Highlander 735, Viking 2S and 3S (both non-cannon), Nightstar 10S
Skye Rangers: Atlas S3, Defiance 3S, Viking 2S and 2S, Nightstar 10S
Kowloon Guards: Götterdämmerung 20S, Scourge WD1, Thanatos 5S, Rifleman 8S, Crusader 6S
Coventry Guards: Fafnir 5, Atlas S3, Viking 2S and 3S, Nightstar 10S
Alarion Guards: Fafnir 5, Atlas S3, Viking 2S and 3S, Nightstar 10S
Bolan Guards: Fafnir 5, Atlas S3, Viking 2S and 3S, Nightstar 10S
Hesperus Guards: Fafnir 5/5E/6E (non-cannon), Atlas II H2, Nightstar 10S
Lyran Regulars: Maelstrom 5S, Uziel 3S/4S/5S, Bushwacker S3
Lyran Unique Chassis: 14 (23 including unique variants)
FedCom Total: 36 (48 including unique variants)