A perfectly good theory...

…shot down by a definitive quote. In Hand Maid May, the genius cyberdoll who applies rigorous logic to all actions (including how much salt to add while cooking) is named Kei, and unlike the title character, gets a -san from everyone. Kei-san = 計算 = “calculation”.

Except the creator came right out and said that she was named after Robot Detective K, who isn’t nearly as photogenic.

He also said that May comes from maid, Mami from mommy, Sara from The Terminator’s Sarah Connor, and Rena from actress Rena Tanaka (This one, not this one).

[…and on an unrelated note, I had no idea that someone was planning a TV spinoff of The Terminator, called The Sarah Connor Chronicles.]