"they already have most of his cards" is a point AGAINST Axel... His only cards we don't have (aside from Volcanic Scattershot and Volcanic Counter, which I doubt will happen) are Fire Trooper, Volcanic Slicer and Burial from a Different Dimension. Even the manga only adds The Blazing Mars, which is also very unlikely.
And if he did, what cards would he have? His archetype is volcanics, which are already released as pack-exclusive cards. No way they give us those cards for free through him.
Technically Volcanic Queen isn't one of Axel's cards. It was used by Trueman against him. (Granted, he was copying Axel's father's deck to mess with Axel's head, but still.)