I love the idea so much. I actually made a thread about Interchangable Movesets a long while ago that was similar to this idea (Though admittedly probably far better and easier then the idea I had in the thread) and I really think this could lengthen the game's replay value more so then any previous Smash game. And all 3 of the previous games on their own have fun gameplay enough for Replay Value even with just default movesets. Can you imagine all the possibilities each character has?
For each of the 34 regular fighters we have confirmed. They have a total of 36 possible combinations EACH. That is a grand total of 1224 special moveset combinations from just those.
But you also have Palutena and the Mii Fighters who are on a completely special Customization level. More so the Mii Fighters. But Palutena also has 36 combinations, but all her moves are different instead of just them being varations of the same move. The Mii Fighters have this as well but not JUST that. Their is three different types of Miis between Gunners, Brawlers, and Swordsmen. But their hitboxes, speed, and strength depend on the height you give the Miis. The customization that the Mii Fighters are astronomical compared to even the combinations all the other fighters have.
And of course we still don't know all the fighters yet! So many combinations to try out. For those willing to experiment and analyze every little fighting combination possible within their Smash Bros games. This is an absolute goldmine.