Rather than having another throw-away character in a Keyhole, I'm hoping that for Volume 74, we'll get our furry feline friend Goro. While not appearing directly, a lot of emphasis is placed on him during Files 775-777. I'd call it a long shot since Gosho has never had an animal in the Keyhole before, but I'd much rather Goro than the maid who will likely not show up again.
As for Volume 75, I think it's definitely safe to say that Miike has that Keyhole reserved. If not, perhaps the Imposter Kogoro, but I'm leaning towards Miike.