I finished my National Dex a little while ago (I think in March at some point). So far, my shiny charm hasn't done me any good, but I'll keep hoping!
At this point, completing the dex is mainly just tedious, not hard. For the people who said they were finding it hard to stay motivated to finish it, a couple of things that helped me were as follows:
-Keep asking for Pokémon you don't have on the GTS (in exchange for breeding rejects or something). You'll inch towards your goal without having to do any extra work. I'd recommend doing this for Pokémon you really don't want to deal with obtaining (e.g., for me, trade-with-item evolutions, some legendaries, etc.). That way, when you do decide to sit down and tackle the rest of your Pokedex, it won't be as daunting.
-Make a list of what Pokémon you still need and group them by category (e.g., breedable Pokémon, catchable Pokémon, etc.). Pick a category and take care of everything from that category (e.g., if you have a bunch of Pokémon that you need to breed, and you have the parents, just make yourself go through a bunch of eggs to get them done).
Now I'm trying to breed 5/6 IV versions of every Pokémon (or at least every evolutionary line). Unlike my National Dex, though, I don't think that one's going to get done anytime soon.