Theory based on text spoilers
Since Organic Dinosaur is a reliable source I have a theory of Floch based on the new spoilers.
Let's just start with the fact that Floch has always been a judiciary person with his own goals and ideology. It's confirmed that he hasn't changed his mind ever since he told Armin he should have better died instead of Erwin.
Floch idolized Erwin, his demon, and he needed another one to fulfil his dreams. That person is now Eren. What dreams I talk about, let me elaborate.
In Marley, Floch desired the enemy to pay for what they've done to the people of Paradis island. At that moment, he appeared to be someone loyal to the SC despite ignoring Jean, who told him not to cause unnecessary casualties. Among many other characters, FLOCH FORSTER deserves an Oscar too. What a BIG FAT LIAR he is. Floch has been planning to rule Paradis for years now. It didn't happen the moment Eren escaped to Marley, no.
My theory is, Floch was the one who convinced Eren to go and act on his own without the SC's consent. What consent, Floch decided to create the Yeager Faction and to defeat the government as well as to convince soldiers, especially the young ones to join them, not the military of Paradis. Floch is a talented speaker, he knows how to manipulate people into believing what he believes.
Do you think it would have taken him a long time to persuade Eren the SC has no power to protect Paradis from the world's hatred? Certainly not. The appearance of Yelena and co. just made Floch's plan to work better, he could promise Eren Zeke would help him, and Zeke's plan would be more effective the SC/MP/Garrison could ever come up with. The military made the biggest mistake by accusing Yelena for manipulating Eren and making him to join their side. I'm not saying Yelena wouldn't have any benefit from joining the Yeagerists, but the plan was definitely not hers. It was Floch's and Zeke’s, Floch could have prepared everything before Zeke arrived to Paradis.
Based on this, we are free to assume Floch was the one who forced Historia to find a partner for conceiving a child, and Floch is the cloaked person. Not only did he need Historia's pregnancy to postpone Zeke's death, but for having time to betray the military and succeed the Yeager Faction's coup d'état. What he’s doing now is kind of similar to what Erwin did to the fake king of the walls. Except Floch not neccessarily wants true freedom for his people...
What I believe is Eren is only a doll in Floch's game and no matter how hard Eren tries to believe he's free and whatever he does is according to his plan, it's Floch's, in reality. And Floch acts like as if he was a subordinate to Eren and Zeke, when he is the one who wants to be the real ruler. Not that he has the power for that, yet.
What if he wants the power of one of the titans? What if he would like to eat Annie despite they may not have any idea whether the Female Titan would work with a man? It's just speculation, but I don't trust Floch at all.
There is a proof that he might be a double agent on top of everything. The proof for that is, Eren wasn’t aware of Historia's pregnancy before he returned to Paradis. He accused Hanji for sacrificing her and he was very furious about that. Hanji didn't even have the time to explain things to him, and Floch... well Floch might have misinformed him or simply just lied about Historia's condition. One thing for sure, if Floch was indeed the cloaked figure who persuaded Historia, Eren had no idea about it. That means Farmer-kun really is the father, and there is a good chance he became a Yeagerist soon after Historia asked him to do the baby job. No wonder why Historia looks so miserable in ch. 107. She truly became a puppet monarch having 0 authority to change anything.
All in all, if Floch truly is a double agent, that would mean he only uses Eren for his final goal. What goal is it is still uncertain. Using the rumbling wasn't his idea.
All of this is only my theory, and as you've seen, based on the proof we have it doesn't seem that far-fetched anymore. Let me be wrong, because if this is all true, Eren might be in danger.
Isayama said that Floch will have an important role in the story. That wasn’t a lie.