trying to argue that this shard needs a buff because it is weak compared to the OP shards is probably the wrong way to go about it. For all we know, zanz might have a nerf in store for SoSa and such.
The change mentioned (allowing this to be played on all creatures, buffing immaterial by +4 atk) sounds pretty good to me. And the momentum thing really isn't a problem. The card says to convert to spell damage, which has always ignored most sheilds; the card doesn't specifically say "ignore shields."
Also, if we stay with such rigid classifications, then antimatter technically should be changed, since it causes the creature to ignore most shields.
SoSa won't be probably nerf (unfortunately). Shards have one big problem, they aren't balanced.
Some Shards gives bonus for specific Element (like SoG, SoD etc), others not or very small (SoFr, SoSe, SoFe).
Few Shards can work with all Elements (SoFr, SoR, SoSe), others has got problem with it (SoW).
Some Shards give new ability/tactics in game (SoW, SoFo, SoSe, SoV, SoSa, SoFe etc.), others changes nothing in game (SoG, SoD, SoFr).
SoR can be used on all creatures, so why SoW not? (argument for buff SoW)
SoFr has got similar skill and it is worst and more expensive than SoW (argument for nerf SoW)
Echh, it will be difficult to balanced all of this Shards...
SoV, SoFr - needs the biggest buff
SoSa - need the biggest nerf
But it is only my opinion.