The processing needs of a wifi connection (or any wireless protocol) are overwhelming on dealing with the problems of a radio connection. Unless you are connecting, sending a single package and disconnecting¹, encryption barely registers.

For wired devices things changes a bit. Encryption can be dozens of times more expensive than moving your data around for processing. But if that's a problem, you need to accelerate your encryption in hardware², not to weaken the encryption.

1 - If you are, you are better with some protocol that keeps the encryption setup around between transmissions, not with weaker crypto.

2 - Just like you accelerate the "moving data around" part, because it doesn't go from the network into the main memory for free either.