Would've been feasible had X-Swordsman Saikou only changes from the upper body much like Geiz Revive whom was the closest to a full un-segmented form change.

Saikou requires changes on the limbs too and those would require taking apart the the figure and replacing limbs, of which could interfere with the figure's durability. It would make more sense to just make a whole new figure.

It really isn't that expensive, considering RKFs are never actually sold at the prices as revealed in the listings. RKF Calibur was initially listed at the same price, too, but I got him from Amazon JP for less than 30 USD.

It's possible that they'll do a Saikou set with Saikou, Saikou's shadow, Wonderful and Powerful. Wonderful and Powerful are relatively small changes on the suit and very feasible for SH Figuarts. X-Swordman would require an entire new mold though, so that wouldn't work.

Red and purple might refer to infrared and ultraviolet light which exist at the extremes of the electromagentic spectrum while yellow is the visible light. As for the book's colors, my guess is as good as yours.

I really think there needs to be WAY more Animal Books. Seriously.
Imagine the animals for those Elements which don't have an Animal Book
Gekido: Maybe a mole?
Hayate: Wolf to complete Kobuta 3 Kyoudai or Chameleon to work with Sarutobi Ninjaden
Kurayami: Squall Vulture to counteract Rekka's Storm Eagle or either Bat or Spider
Suzune: Either Bat or Pistol Shrimp because they are both related to sound.

Yeah, but we already came off a season with a LOT of animal-themed collectibles, so the higher ups probably don’t want to do animal items heavily two years running (especially since the three from the Swordriver combos were all done in the last toyline)

I'm wondering if the SHF will have parts swapping, not the RKF.

I guess. Except for Storm Eagle. There might have been "Dynamiting Lion" as a counterpart to Lion Senki and "Gatling Hedgehog" as a counterpart to Needle Hedgehog, but there was no *verb*ing Eagle Progrisekey. And Flying Falcon doesn't count as it was based upon a falcon and not an eagle. And anyways, looking at the animals I thought up for each of them, the ones with Progrisekeys based upon the animals I listed off are Wolf (Shooting Wolf) and Spider (Trapping Spider). If you were to even consider the Zetsumerisekeys, the only one which was given that treatment was Bat (Onycho Zetsumerisekey). There was no Mole, there wasn't a Vulture, there wasn't a Chameleon, there wasn't truly a Bat, and there wasn't a Pistol Shrimp. There was only the Wolf, the Spider, the Lion, and the Hedgehog. And anyways, look back at previous toylines with gimmicks based upon Animals (OOO and Build). It isn't exactly like they don't use Animals. If you were to compare the list of Animals used in the Progrisekeys to the Animals used in the O Medals and the Biotic Fullbottles, you would find a lot of overlap. In fact, the amount of animals used in the O Medals
and the Biotic Fullbottles, but not the Progrisekeys is even more numerous. For this, I will not include any of the Zetsumerisekeys as those won't count. Here is just the O Medal Animals and if they have a counterpart as a Progrisekey or a Wonder Ride Book.
O Medal Animals
Taka (Hawk)
Kujaku (Peafowl)
Condor
Kuwagata (Stag Beetle) - Exciting Stag
Kamakiri (Praying Mantis)
Batta (Grasshopper) - The first O Medal Animal with a Progrisekey version in Rising Hopper
Lion - Dynamiting Lion and Lion Senki WRB
Tora (Tiger) - Flaming Tiger
Cheetah - Rushing Cheetah
Sai (Rhinoceros)
Gorilla - Punching Kong
Zou (Elephant) - Won't count Breaking Mammoth as that is a Mammoth, not an Elephant
Shachi (Killer Whale/Orca) - Not Splashing Whale as that is more of a Blue Whale
Denkiunagi (Electric Eel)
Tako (Octopus)
Cobra
Kame (Turtle) - Not Tortoise so Genbu Shinwa WRB doesn't count
Wani (Crocodile)
Sasori (Scorpion) - Sting Scorpion
Kani (Crab)
Ebi (Shrimp)
Same (Shark) - Biting Shark
Kujira (Blue Whale) - Now that is Splashing Whale
Ookamiuo (Atlantic Wolf-Fish)
Shika (Deer)
Gazelle
Ushi (Cattle)
Mukade (Centipede)
Hachi (Bee)
Ari (Ant)
Seiuchi (Walrus)
Shirokuma (Polar Bear) - Freezing Bear
Penguin - Storming Penguin
Yadokari (Hermit Crab)
Panda - Scouting Panda
Kangaroo - Hopping Kangaroo

Meanwhile, here are the Biotic Fullbottles and their Progrisekey/Wonder Ride Book counterparts.
Rabbit
Gorilla-Punching Kong
Taka (Hawk)
Panda - Scouting Panda
Harinezumi (Hedgehog) - Gatling Hedgehog and Needle Hedgehog WRB
Lion - Dynamiting Lion and Lion Senki WRB
Dragon - Brave Dragon WRB, Jaaku Dragon WRB, basically all of the Dragon WRBs (Though these aren't Animal Books)
Octopus
Phoenix - Burning Falcon and Eternal Phoenix WRB (not an Animal Book)
Wolf - Shooting Wolf
Unicorn
Turtle- Again, not Tortoise
Kabutomushi (Rhinoceros Beetle)
Kuma (Bear)-Not Polar Bear
Dog
Spider - Trapping Spider
Tora (Tiger)- Flaming Tiger
Kujira (Whale) - Splashing Whale
Shika (Deer)
Kirin (Giraffe)-Sparking Giraffe
Penguin - Storming Penguin
Same (Shark)
Bat
Hachi (Wasp)
Sai (Rhinoceros)
Lost Bottles
Spider- Trapping Spider
Cobra
Kuwagata (Stag Beetle) - Exciting Stag
Fukurou (Owl)
Shimauma (Zebra)
Crocodile Crack
Scorpion - Sting Scorpion
This shows that they had a HUGE List of Animals due to the O Medals and the Biotic Fullbottles. But they didn't use most of these Animals. And this shows that, oddly enough, even though there was a Taka O Medal and a Taka Fullbottle, there was no Taka/Hawk Progrisekey.
The Progrisekey originals for those animals which weren't given O Medals or Biotic Fullbottles are Flying Falcon, Amazing Caucasus, Lightning Hornet, Amazing Hercules, Crushing Buffalo, Fighting Jackal, and Invading Horseshoe Crab. The only Wonder Ride Book Original Animal that wasn't given any of the previous gimmicks was Storm Eagle. So, the list of real birds which have inspired a Collectable Gimmick at least somewhere in Kamen Rider is Hawk, Peafowl, Condor, Penguin, Owl, Falcon, and now Eagle.

Sorry for listing off ALL Animals from Collectable Gimmicks in the past. To have a TL;DR, it's just that there are SO MANY animals used in the Kamen Rider Series with all of these Collectable Gimmicks that NOT using an animal which has inspired a Collectable Gimmick in the past. So, yeah.

11 main swords and few main base books probably appears in silhouette . I guess southern base use generate man made sword perhaps not part of main ones Judging there's 7 of them. It looks like primitive drgaon can take control blades or anyone book as well. Reika and three bad along with desast is still generic blueprint character profile with not a lot of materials to go for. Every epsiode is the same for them.

Personally I think they'd do what they did with Evol's SHFs; first they release Saikou Shadow, and it comes with the parts to swap for the shield and leg modes of X-Swordman, plus swappable Saikou Drivers (one w/o the X-Swordman WRB and one w/ it) and pieces to change between the Kin no Buki Gin no Buki WRB's rider page and sword page to accommodate for when you're using the X-Swordman parts. And then they release the full body Saikou X-Swordman SHF like how they released the Evol Black Hole SHF.

I do still think there should be more animal Wonder Ride Books. If it's only about five more, that should be a notable increase and still keep the collectibles from being animal-heavy.