Thematically, I believe it makes sense that necromancers should have some source of darkvision. I would like to propose 2 possibilities for adding this to our repertoire:

"Through transfusing a kind of gaseous growth in the eyeball, the spell effectively hones one's sight to greater keenness."

1) Add it to Kura-Silma: In addition to +perception and +attunement, the greater keeness would also lend to being able to see in the dark. In comparison to "Tenebrous Sense" (costing 1 spell slot), I believe this would be a reasonable add-on without an additional cost of a spell slot especially taking into account the known negative consequences of using transcendental magics.

2) Add it as metamagic to Kura-Silma: Greater keenness would also lend to increased accuracy with ranged weapons. For 1 spell slot as a metamagic (similar to Chiruirga), we could have darkvision as well as +ranged accuracy. This would have a similar spell slot cost to "Tenebrous Sense", but with the additional spell requirement of Kura-Silma. Additionally, this gives a perk to necromancers that prefer to use ranged weapons, and doesn't force everyone into small edged weapons.

Thank you for your time.