A little follow-up regarding Silvadi and its possibly being an equal of Arceus, instead of being a poor-man's version of it:
I am pretty sure people have noted that Silvadi's name is derived from Shiva, the Hindu deity. Much like Zeus, Arceus' supposed namesake, is the prime deity in Greek mythology, Shiva is the prime deity in Hindu-ism. The Wikipedia entry for Shiva reads:
"Shiva is "the destroyer" within the Trimurti, the Hindu trinity that includes Brahma and Vishnu.... In the goddess tradition of Hinduism, the goddess is described as supreme.... At the highest level, Shiva is regarded as formless, limitless, transcendent and unchanging absolute Brahman, and the primal Atman (soul, self) of the universe."
Much like Arceus is noted for being the "creator" the Pokemon universe, Silvadi's Shiva is noted for being mainly the "destroyer". The "limitless" remark matches the Japanese description for Silvadi as well.
As Sun/Moon has been said to have heavy alchemy themes, I think it is not a stretch to believe that Silvadi is the culmination of alchemy - the goal of humans to achieve something as close to God as possible. Whoever created Silvadi (Team Aether?) must have seen to it that its power is sealed by creating Type: Null. There has not been a precedent where a man-made Pokemon is designed to be "weaker" than it is supposed to be (although there is a man-made Pokemon becoming "stronger" than designed a la Mega Mewtwo), which meant that Silvadi must have been a very successful creation for the mask limiter to be necessary.
Another thing I am very interested in is the connection between Silvadi and "memory". It certainly sounds a little robotic when one thinks about it in the computer memory sense. However, as Gamefreak is being very clever lately, I suspect that the word memory might have another meaning - alluding to a certain game mechanic introduced in Generation VI.
Finally, there is also this thing about Type: Null evolving when it finds a trainer it trusts, suggesting that it does not evolve by leveling up. However, I find it hard to believe that it is implying Friendship- or Affection-based evolution, as a Pokemon that is supposedly as powerful as the legends should not be unlocked with such an easily exploitable evolution method (you can evolve before level 10 with these sorts of evolution!).
If all my speculations are not misguided, that: a. Silvadi is basically an Arceus equivalent (or above), and b. Silvadi will put the memory mechanic to good use, then it might be the case that Type: Null evolves upon unlocking a certain memory with its trainer. It has certainly not been done before, and I suppose it is a guarantee that Type: Null will not evolve prematurely before reaching a certain point in the game. Would be pretty anti-climactic otherwise.
So many things to speculate about this one Pokemon. Getting very excited about Sun/Moon!