My suggestion is that with all the new ideas and concepts to take on board, it may start to ruin the game a little. Adrenalyn Xl for example has, in my opinion too many card types of a poor quality as well as a bad design. For me, that ruins the collection, and while the addition of a new card type may be a good idea (paticularly the legends which we are used to having by now) we don't want to spoil it.
So my overall suggestion is to improve the quality of the collection. After all, quality over quantity. I think it would really boost the appeal of the collection if the MotMs for example could be improved, and as they are already good now, making them better would make Match Attax look even more like the superior collection. Thanks for reading