I see mostly good in this decision...but could bring me see some bad later.
The good is that it really doesn't change the gameplay that much. Holding a button and rapidly pressing a button for a combo is going to be about the same speed. Specially when you realize you can tap a button faster than the animation can play usually.
This will not hurt the balance of the game, or take skill away from the game. BUT, it will make the game more accessable to all controller types, all types of gamers (non, advanced, novice) and potentially open the game to some combo options.
Now you can potentially begin a standard combo, and then move forward, down, up, back to tack on a strong attack, and just flick to add a Smash. This WILL make the battle system easier, but we are talking about a 4 player game that is not about defeating an enemy by depleting their health. It is a game about area control, and fighting several opponents knocking them off the stage.
I don't think this inclusion is anything like the C-Stick Smash either. That mechanic allowed for you to pull off Smash attacks too quickly and easily. Making it harder for those that don't use that method to get their Smash Attacks in...which is the driving mechanic of the game. Standard combos and attacks are not the driving element of the game, only the Smash attacks are in my opinion, and I hope since they include this simplier combo system and they are trying to balance out all control methods, that they will remove the C-Stick Smash so that Wiimote users can have equal balance.