Let's say that Isabelle was put into the game and Vergeben was right. Would she be an echo or a brand new character?
A completely unique character.
Note Sakurai's statement about non-combatants way back in a
Kotaku Smash 4 interview:
“An important thing is that the characters stand out from one another—for instance, we might wanna be able to take characters that aren't typically combat-based characters. So you might have a sword-based character, but other characters are not necessarily going to [have swords]. You're not gonna wanna focus on that sort of element, just so there's a distinction between all of the other combat-based characters.
They have to have something really unique that makes them stand apart from other characters in the game,
and not limit yourself to characters that are just combat-based.”
And note how Sakurai researches deeply into gameplay step-by-step to find distinct traits of a character:
“The first thing is to take an idea. For example, imagine a game and character within that game. Take a character such as the villager in
Animal Crossing. The next process is think about that character's role in their game and then the structure of the game we're making. How do those work together with each other? What kind of interesting things can you do within the structure of the game? And then if you were to actually implement that character, how would the end result be, how it works with other elements of the game?”
The thorough research Sakurai does to find a character's potential even in non-combatant Nintendo franchises makes me confident that he will find solid moveset potential in Isabelle. Isabelle provides a plethora of moveset potential, when connecting the new gameplay mechanics/features of New Leaf with the character not covered by Villager. Whereas Villager uses a set of tools and items a player can utilize in Animal Crossing (Axe, shovel, Pocket, slingshot, etc.), Isabelle would use Public Works Projects and possibly town laws to make her playstyle/moveset standout. Finding her potential would not be a difficult task.