I'm kind of worried, too. I barely have anything on my phone just to make room for all of the updates we get, but I still wouldn't be surprised if told me there wasn't enough space when GX. And then what? 5Ds? Xexal? I guess I should buy a data/memory card or something.
At one point i had both yugioh duel links AND Skyrim Legends 1.8GB (another great card game) on my phone and another 1gb online fps game and everything worked fine.If yugioh continues getting bigger, fine with me.Buy an SD.