... makes sense but can go both ways in terms of what he/she represents, theres a lot of stuff that hasn't been covered yet, and it wouldn't feel right for a pony like, idk... lets say pinkie, have an episode that doesn't fit her element, it wouldn't feel right. A new pony however, may just make the possibilities expand, and just because its a new element doesn't mean it HAS to be part of the mane 6 as soon as its introduced, it could be a completely new pony at first, and slowly gain friends bit by bit, maybe every two to three epsiodes to make it look a bit more natural, and show at least SOME conflict before befriending said pony, and then boom, we have a new element in the cast
and plus, a new element = extra pony.mov episode AND new Fighting is Magic character!
But i can also see where it may fail.
Maybe the element isn't really that necessary for the cast, or its just too typical, say its the element of... idk lets say focus, in contrast with what i said in the last paragraph, a pony may already be fit to learn a lesson on the element of the new pony in its entirety, we would just end up with another pony just being there, it might have a distinct personality, but it would just be... there...
overall, i feel as if it depends on how the new element will adapt to the others, and what it is
... I Talk A Lot...