I am a full-time kayak user and personally have no interest in making a small plastic boat into a motorized craft. If some other user wants to do that, feel free. But at some point, you lose the advantage of a lightweight, easily transportable vessel that can sneak into very skinny water.
Several companies make electric motors specifically for the kayak sector, but they don't push a boat at 20 mph. I have fished with kayak guides who have electric motors on their kayaks. They can tow clients over longer distances to reach new fishing spots. I understand how motors can be beneficial to guides. I know of some recreational kayak anglers who want to have the longer range provided by a motor-propelled craft. That is personal preference, but is not for me.
There are micro-skiffs like Solo Skiffs that are not much larger than kayaks and use a gas engine. Americans love to "pimp their ride" and customize any type of vehicle so it is a bit different from anyone else's vehicle. I see this type of product as appealing to that niche. In past years I have owned two different Gheenoe models. These are small, slender, basic boats that use outboard motors, but should not be confused with kayaks.
The Mokai hull design mimics a sit-inside kayak (portions of the hull are covered, with an oval opening to sit in. This style of hull is common in recreational and touring kayaks, but is generally not favored when using kayaks for fishing. Instead, a sit-on-top hull design is far and away the most common.