I have a feeling that Kaido is going to end up being an Awakened Zoan or something along those lines. Everything points to this guy being 1. A monster literally and figuratively, and 2. Someone that you don't back out of a deal/agreement with no matter the circumstances. What Law is doing to Doflamingo is that he is making him sever his ties with the WG. We all know that Doflamingo works with some very high ranking WG officials, but we also know that the new Fleet Admiral Akainu despises pirates which includes those of the Shichibukai. Doflamingo leaving the Shichibukai, especially for no apparent reason, would catch the attention of the WG but especially the Marines, including the Admirals as Law noted.
Any way you look at it Law is really quite a cruel individual, he likes to play around with people as much as anyone we've seen. But i will say this much, Oda is working very hard once again in showings us how much Doflamingo's crew cares for him, but more importantly how much he cares for them. He told Baby 5 and Buffolo not to worry about apologizing since they were following his orders, and the first thing he asked Law was for their bodies. This may be subtle as this point and not mean a whole lot, but i think its going to be very important when Doflamingo finally begins to move against Law and Luffy.
We don´t know the exact definition on how to become PK (well, most think that finding OP makes you automatically PK), nor do we know whether DD believed in that or had another image of what a Pirate King is since he rather seems like a realist who would not believe in any ominous treasure. Either way, everything he did so far certainly increased his power (becoming a Shichibukai, becoming a broker) but it did not really help him get closer to being the PK. If he thinks that PK is the one who stands above all other pirates, then beating the Yonkou would be the goal which pretty much is the opposite he was doing the last 2 years, namely helping one to get stronger (unless there is something wrong with the Smiles). If he thinks finding OP makes him PK, he still did not really do something to achieve that, thus i am a bit disappointed in the characterization of DD after the TS.
I won't neglect a possibility of zoan but it's also possible he's just ferocious and violent. Perhaps his fighting style is what makes him a beast/thing. Maybe it's because he doesn't leave anyone alive, like he did with Moria's crew. He could also have a paramecia ability which gives him some kind of bestial power.
If it's an awakened zoan like those in ID, I don't see it happening. Unless he's an awakened awakened zoan, one who looks like an animal but has more inteligence than those and can actually talk maybe.
But, as far as I'm concerned, Oda showed Kaidou here (in the top left, don't know who else it should be):
and he looks like a human. An angry human with epic mustashe. God I hope he's not a giant, would make a boring battle.
the idea i had was:
imagine that Law knew DD from a young age and idolized him the way Luffy idolized Ace or even Shanks. Law grows up, becomes a pirate and decides to follow DD's command. Law then becomes deeply disenfranchised by DD's tactics and becomes increasingly disappointed by his refusal to confront any big shots and his insistence on making deals with them.
Law gets fed up with his one time idol or hero, if you will, and decides to take matters into his own hands and plans this elaborate scheme to force DD out of hiding and force him to be a pirate once again.
Not even a human makes me think he is probably a result of an Artificial DF like that of chopper, maybe a dragon or some norse creature that gives it human like abilities.
Else, Kaidou could be an alien, or a creature that fits that description. And the ship we saw that pulled up Capone Bege's ship, the one that looked like a UFO could be Kaidou's ship.
There is really no point in calling and describing Kaido as a monster/beast/creature/thing if he literally wasn't something like that. WB was called a monster at one point, but that was a reflection of his power and not a reflection of what he was. They referred to him as a man/human when speaking about him. So Kaido is either some type of a "normal" beast with a high level of intelligence like Bepo or he is something like an Awakened Zoan. Otherwise i don't see the purpose in calling him everything but a human, talking about him wanting to create a beast like army, and giving him the nickname of a Hundred Beasts.
Is it possible that Law is blackmailing Joker just out of spite, as opposed to as part of his plan, and that he has no intention of giving him Caesar back? It might be that he needs Caesar for making a deal with Kaido or something, and he doesn't really need Joker to step down from Shichibukai, just dislikes him and wants to make his life a misery. Although, either way it's in Law's best interests to weaken Joker as much as he can so he doesn't try to intervene with his plans or get revenge.