i guess Pako felt it was too strong... Just the idea of it does sound reeeaaaalllllly good tho lol
Either that or maybe now it has spear's proprieties, in MK9 on the tag mode there were moves who shared usage proprieties, like Sub-Zero's Ice Ball and Scorpion's spear and Cyrax Net, you couldn't do a combo using the two moves without reseting the combo, if you used the spear, you wouldn't be able use freeze or net in the same combo, it would count as if the move were used before.
If in MKX spear and Flame aura share the same propriety then Scorpion can't use his spear as a combo starter then use flame aura as a combo extender and if Scorpion use Flame aura as a combo starter then he can't use Spear as a combo extender, using the spear afterwards might trigger as if it was used twice and the spear ender animation would just pop up.
Maybe Pako could confirm, but he is this busy that i would feel blessed if he could take sometime on this matter.