Hold on. "It also states clarifications about the demo version of the game. You will see a Mega Evolution for the first time in this demo, and you can then transfer it, as well as items you collect, over to the main games when they are released. It is also hinted that,
if you play the demo every day, something special will happen." -Serebii.
Now, let's remember that the demo starts in Mossdeep City, the home of a certain space center...
"In the games, a man by the window will reveal the number of successful launches there have been; the number is an indicator to the number of weeks since the saved game was begun. Because this is a time-based event, the Space Center will cease to launch Rockets when the battery for the internal clock runs dry.
Many rumors have been spread about this number and its relation to
Jirachi and
Deoxys. Many believe that if the man reaches a certain number, the player will be able to ride a rocket into space and battle Jirachi or Deoxys." -Bulbapedia's page on the Mossdeep Space Center, under the Rumours section.
We have a demo with a bonus event if you play for enough days, a demo for the remakes of the first games in the same generation that referenced the Mew Truck rumours. I can totally see Nintendo making it so that in the end, those rumours somehow got the last laugh!
...If somebody else already thought of this and posted it
without needing a huge wall of text, I am going to feel really stupid.