>What’s more, the DARPA program calls for the tech to be bidirectional; the implants must be able to not only record signals, but also to transmit computer-generated signals to the neurons. That feature would allow for neural prosthetics that provide blind people with visual information or deaf people with auditory info.
What's being described here is the key to full-dive virtual reality. With this you wouldn't even need waifubots. If it's able to tap directly into your senses the entire experience can be virtual. Everything then becomes a matter of software and digital content.
Then again you probably still need a physical robot if you want her to cook and clean for you, but even that's debatable. This technology should in principle be able to do Augmented Reality too. So you could have a roomba vacuuming your floor but AR makes it look like she's doing it. Or you might have an automated kitchen preparing your meals but make it look like she's cooking for you.
Parts of the human mind could go into making a waifu personality. Things like base level intelligence. But the personalities of waifus are largely artificial. Kuuderes, Tsunderes, nobody acts like that IRL? Their personalities would still have to be programmed or trained into an AI.