It could be a split evolution from Porygon2. Dubious Disc (Not made by Silph Co.) makes Porygon-Z, so it stands to reason that an official silph Co. upgrade could be made to make Porygon3.
And this time..
IT WILL OPERATE IN SPACE.
What would it's stats be like? Abilities? And more importantly, what would Conversion3 be like? --- PSN: Blackcat012 3DS FC: 0834 1716 7409 Trainer name: Albert Your friendly neighborhood black guy who may or may not steal your bike, at your service!
Conversion3... it'd be neat if it randomized the types of everyone on the field! And they could give it a stance-change type deal with its stats to make it even more gimmicky. Perhaps switching between an atk/def form and a SpA/SpD form? --- You can say "ass" on GameFAQs. Assy ass ass assington.
I think there should be a porygon3 because like you said PorygonZ is just a virus and not really the next stage in its evolution. Also I think Porygon3 should look more like an animal. If you notice Porygon goes from a boxy artificial pokemon to a more realistic bird like pokemon as Porygon2. So I always imagined it getting more and more real and life like as it evolves.