Pretty sure it's not pre-order bonus, it's just a timed exclusive Mystery Gift, like Torchic holding Blazikenite for XY and the Shiny Beldum with Metagrossite for ORAS, being only available for a "short" period after launch.
There's a big difference between a Pokémon with a shovel in its design, and a Pokémon with its design based on a shovel. I don't think anyone would look at Sunabaa and/or Shirodesuna and think "Yep, that Pokémon is based on a shovel."
All Legendary Pokémon catchable in ORAS can be shiny (with the excception of Groudon, Kyogre, Rayquaza and Deoxys) even Reshiram and Zekrom, which I've personally SRd for and caught shiny.
The GS ball was used to obtain Celebi in Gold and Silver (+Crystal?) but was only available in Japan. The anime dropped the GS ball storyline because of Celebi's role in the 4th movie.
A better example would be the God Stone in Black and White, though that was unobtainable.
RE: Get the Eon Ticket via StreetPass! Only if you live in US?
The UK distribution is already confirmed, as are many others.
You can find out what other countries are doing it simply by changing the region (Select a Country) on the link you posted.
You do realise that the PSS is able to interact with the pc from the field already (see the GTS). It wouldn't be much of a stretch to abolish the pc system altogether and just let the player interact with the pc system anywhere. No need for the player character to carry around some huge device...
RE: Return of the Secret Base!
If you connected with someone via a link cable their base could appear in your game. You would be able to battle the person inside the base with whatever team they happened to have at the time when you connected. Not sure on the specifics of how to cause this to...