Magicka classes usually have an offensive ultimate in their kits, Soul Harvest for magblades, Crescent Sweep for magplars, Ferocious Leap for magdks, Overload (lol) for magsorcs, Permafrost for magdens and soon Glacial Colossus for magnecros. Then there are non class specific ultimates like destro ult, Meteor and Soul Assault.
Right now the gold standard of offensive ultimates is Dawnbreaker of Smiting, so good that even some magicka classes like magsorcs and magplars use it because it packs everything needed for PvP: relatively cheap (125 ult), AoE, big burst damage, stun, big DoT and bonus damage to vampires and werewolves.
None of the magicka options I have enumerated come close to DBoS in my opinion except Leap maybe. They are either not really suited for some playstyles like Soul Harvest for magblades who want to stay fully ranged, very costly though deservedly so as they are good to great options for group PvP (destro ult, Permafrost, Meteor, Frozen Colossus), very telegraphed (Meteor, Soul Assault and to a lesser extent Frozen Colossus), or just underwhelming like Crescent Sweep and Overload.

So I'm asking for a rework of Shatter Soul into a cheap ranged burst damage ultimate for magicka players like Dawnbreaker is for stamina players, I don't think I've ever seen this morph in my death recap so it seems the best candidate for it. High Kinlord Rilis from Banished Cells I uses a skill named "Soul Blast" that looks perfect as a working base for such an ultimate: a high powered, very slightly telegraphed projectile that stuns. The stun could be replaced with something else like a DoT or some splash damage (like a 5 meters radius).

I would really hate to slot Dawnbreaker on my magicka necromancer like on my magsorc because the Colossus, while good is just too costly and not as easy to use, and I already use Dawnbreaker enough when I'm playing stamina characters.