All Psychic Type Pokemon either have to do with mind-based powers or space/cosmic energy. We shouldn't confuse cosmic and astrological energy with magic because there is a sense of science behind it (think: Alchemy).
The reason for that is because there isn't an alien/cosmic type, so all alien pokemon are shoehorned under psychic.
Light + Cosmic + Magic = Fairy, Tech = Steel + Electric
The only POSSIBLE type you listed is Sound, which due to popular demand may see light in 7/8 Gen.
So Porygon should be an electric/steel pokemon?
Sure, you say this now, but if/when GameFreak unveils a new type and it's not sound, you'll recant your position in a heartbeat. There's just as much demand for Cosmic and Light and Cyber as there is for Sound.
Porygon should be electric, since the energy aspect of technology is electricity, and robotic pokemon should be Steel-type on average, as long as they're actually made of a metal. Golurk can learn some electric moves because of it's robotic elements, but Tech wouldn't really work because Tech implies usually something made of metal that's powered by electricity. If you look at the Pokestar Studios robot props, they're Elec/Steel, so anything Tech-related will undoubtedly be Steel/Elec or some less expected combination like Golurk's. Only two moves have been shown for Fairy-type right now: Moon Blast and Fairy Wind. Moon Blast has to do with cosmic powers, which Psychic and Dragon tend to cover already. Moon Blast also can be looked at as an example of a light based attack, also under Fairy. Fairies are magical creatures: in mythology a lot of their power is based around magic. Also, they tend to be either good creatures often representing light, or bad creatures of darkness, which of course is already covered by Dark-type, so any Light-type speculation is likely wrong. If any more was added to cosmic-based attacks, they'd probably be Special based of Rock, Psychic, Dragon, or Fairy.
Edit: this also can be added to by Nate's above statements.
Edit 2: Technology consists of hardware and software: hardware being the physical parts, software being the electrical signals that are interpreted into code and programs, like nerve signals in the brain. This "software" aspect is the basis of Porygon.
I'd like some pokemon to have their own exclusive type such as maybe Palkia having Space type or Celebi and Dialga having Time or Chrono type. Also Psychic type isn't necessarily about psychic powers, it's more about magic on the whole so perhaps a fix for that. The two types people were speculating for Xerneas and Yvetal, Light and Sound, would be good ones to have as well, although it would need a fix for some moves such as screech, light screen and flash cannon
I of course would love to have my own exclusive Type! However, Steel-Type is too awesome to give up, and I'm a bit too Dragony to not be Dragon-type: however, if they made a Dragon Aura ability (which speaking of Aura abilities I predicted them since Gen IV), I would take that over Pressure in a heartbeat to have my own Type.