After now rewatching the new episodes for the umpteenth time, I happen to notice that Twilights new wings were larger then Rainbow Dash's wings

I would surmise that by examining the other Alicorns, that the wings would have to be larger then a normal Pegasus and again I go back to the argument of bone structure.

A normal Pegasus like Rainbow Dash, would have to extreamly light weight in order to archive flight and thus would need hollow bones to reduce weight without the comprise of strength and thus wouldn't need of large wings.

But an Alicorn is much larger and heavier than a normal Pegasus and would need larger wings in order to archive lift.

Twilight, although she's the same size as Rainbow Dash, she started life as a Unicorn and thus had more solid bone structure and thus needs larger wings.

I have always been an advocate of the hollow bone structure of normal Pegasus and seeing this difference in my opinion confirms this hypothesis.