Interviews leading up to the season have made it pretty clear that The Flash villain, the Thinker, is not a speedster. In the first few episodes of Season 4, the Thinker is not running or walking around but seated in a floating chair, attached to a variety of wires. This lack of speed and even movement doesn't make him less ominous than other Flash bad guys. The Thinker appears to be playing with the good guy team in a metahuman chess game that won't end well. Still, his immobilization is highlighted. Is it possible the Thinker is really a speedster? This fan theory isn't that unbelievable.
Executive producer Todd Helbing spoke to Variety about the changes made for Season 4 of The Flash. He specifically talked about this season's villain not being a speedster, unlike the villains in Seasons 1 through 3. He said:
"The Thinker has been a guy who’s been on the board since Season 1. When we knew we didn’t want to do a speedster, there was such a breadth of new challenges that somebody with super intelligence could pose to Barry and the team. His powers sort of allow us to not have Barry fight the same sort of villain."
There is a specific emphasis in Helbing's statement about wanting Barry Allen to fight a different type of villain than he's faced before. (Villains like the Reverse-Flash, Savitar, and Zoom.) Making The Thinker a speedster would go against this expressed desire to branch out. Still, the theory isn't entirely unfounded.
On the Reddit Flash discussion page, user Professor_Jiggy posted their theory that the Thinker was a speedster whose body got crushed beyond even speedster healing, but whose brain retained its superhuman speed. Barry can read with increased speed ability and is hyper intelligent, and yet, the Thinker still has a faster mind than him. This could be chalked up to a separate metahuman ability, but could also be a speed-related outcome. If the Thinker was a speedster at one point, than all his speed is now focused in his brain, making his thoughts even quicker than before.
A second part of this theory is that The Thinker wants to take Barry's body and combine it with his mind. The mysterious symbols Barry was writing when he emerged from the Speed Force also appear on The Thinker's cheek, potentially connecting the two in a deep way. This connection because of the symbols is the most interesting part of this take and may emerge in some way later in the season.
There is still a lot unsolved about the Thinker, including where he comes from and what his motives are. So almost any theory could become reality. Still, this speedster idea would go against what producers have said they want from The Flash Season 4 and what is originated in the comics. The DC comics version of The Thinker was intelligent from an early age and devices like the "thinking cap" enhanced that, but The Thinker was never a speedster. Of course the TV Flash has strayed from the comics but these origins may debunk this theory.
Every season of The Flash so far has taken its time revealing details about the season villain, and Season 4 is no different. We know that the Thinker is tracking the new bus metahumans he set up to be created. He's keeping an eye on Kilg%re who can control technology and Hazard who causes bad luck. The Elongated Man was revealed as a bus metahuman as well, but Team Flash got to Ralph Dibny first. Beyond tracking these new metas, the Thinker's overall plan is still unknown and his reason for fighting The Flash is unclear.
According to The Flash Season 4, Episode 7 press release, The Flash and The Thinker will come face-to-face and new information will be revealed in the Nov. 21 episode. The synopsis reads:
"Barry (Grant Gustin) comes face to face with DeVoe (guest star Neil Sandilands). Devoe’s past is revealed through flashbacks. Meanwhile, Iris (Candice Patton) puts the final touches on the wedding, which is a week away."
If the Thinker is a speedster it would be a major twist. This meeting could provide major clues about where the Thinker comes from and it will probably narrow down the viable fan theories about The Flash Season 4.