TL;DR If not a tank spec a ranged dps spec could be feasible in my eyes.
So I have some gripes with the 3rd spec for the Evoker.
First I personally advocate for a tank spec. Specializing in the Earth, Fire and Shadow schools while borrowing small amounts of the other elemental schools since the whole idea was for the race to be a mixture of all main dragonflights.
Secondly if we are to go off of the whole point of this post and it NOT being a tank spec the most logical conclusion would be that it'd be a dps-spec. But would it be ranged or melee?
Considering that the other two specs already primarily features schools of magic from the other 4 major dragonflights it'd be logical to think that this 3rd spec would utilize Earth as its primary school of magic so if we brainstorm what a ranged or melee dps class would look like that utilize Earth as its primary school of magic we mostly end up with something like this:
A ranged dps spec focusing primarily on Earth-based spells, possibly taking Shadow and Fire as it's secondary schools of magic I can see be distinct enough to be it's own spec, even if it would impede somewhat on the Elemental-spec for similarities.
A melee dps spec focusing primarily on Earth-based spells seems way too similar to an Enhancement Shaman if you just take away/change their primary school of magic from Lightning to Earth.
Naturally you can brute-force it a little to make it work somewhat but I feel the feeling of gameplay will be too closely related to Enhancement to make it feel unique.