I like the concept, however it'll need some defining feature to be competition between choosing it or the Dark Briar Barrage for your loadout.

Split normal/piercing isn't a bad idea, except there not really being a need for it. Would the normal part of the split damage help it against enemies that are resistant to piercing? To me the only reason the Ionized Salt Bomb is disowned is the charge time. I can plant two Radiant Sun Shards in the same time it takes to plant an ISB. I would use that bomb in a heartbeat if it was just a tid-bit faster.

I don't know so much about the knockback, but I can definitely see the bomb stopping anything it hits in its track a-la interruption just like how the lichen colonies do that to knights. DR and the mist bombs do have that initial explosion but it doesn't actually have knockback. Though if it's too much weaker than Barrage/Nitro then people might pass it up. Exchanging damage for strong interruption could be a nice trade off though. I could have a lot of fun with that against hordes of...well...everything in the Snarby SL :) As for damage per spike or whatever, think of how the spikes happen for the lichen. They don't really progress out like a brandish charge. They happen pretty much all at once. I would see the damage as a one-shot value that effects anything in the "line of fire" of the spikes.

If you were aiming to use the random pattern as a drawback to the bomb then disregard this paragraph, otherwise keep reading~ When it comes to the effected surface area of the blast, think of the RSS. Just like the RSS the jelly attack goes in eight directions last I remember, however the orientation of the attack is related to the direction the lichen is facing. Do the same thing with the bomb so that it has the eight direction attack that depends on the direction of the knight instead of a random pattern.

I'll give my +1 for the concept and new bomb mechanic. It could be neat to implement. I look forward to any concept doodles.