Except you know, primal mantle sky/thorn ends up being one of the better ones for an EK and is only getting better with the +3 imbue dice of shared mantle. So you gear for upto 3 elements. Also you only need to gear for the spell power and not the spell crit.
Cold and electric is conveniently paired most of the time.
Stop being obsessed with the elemental strip fire tiefling ek build it isn't the end all be all.
Fortunately in regards to scion feats it tends to only be a difference of 10 spell power as most are 30 universal 10 specific. Most of the power discrepancy is the crit damage.