I think it's very much possible that the 100,000,000 goal can be met by the 12th. Sun/Moon sold ~10 million copies in its first week, so if every single one of those copies participates, that means everyone would have to catch just 10 Pokemon. Only ten.
Now of course, not everyone of those copies will participate, and not everyone participating will catch 10 Pokemon, but at the same time more and more people will keep buying and playing the games, and some will catch more than 10 Pokemon.
At the moment we're at 1.79 million, which is while less than 2% and not terribly inspiring, not bad for not quite 3 days. I've only caught 2 myself during this time, but I'm pretty sure I'll end up completing the main story sometime before the 12th and then I'll probably end up going on a catching spree and get that number a lot higher.