Some more cards I've been putting into this deck:
Seeds of Innocence: destroy all artifacts, controllers gain life = to converted mana cost
Jungle Shrine makes: r/g/w
Primal Command: target gains 7 life + get a creature.
Reverent Silence: everyone gains 6 life, destroy all enchantments

Some I'm considering:
Energy Bolt: (x damage or x life to anyone)
Evolution Charm: (return a kavu, make it fly over deathtouch)

Some I cut:
Eladamri's Call: too slow/costly
Wall of shards: useless without a kavu - I may go back to 1)
Altar of Bone: don't have enough creatures to sac, other fetches are better

What I'm looking for are more creatures that have useful effects, since I have 8+ creature tutor cards.  I have 1 birds in right now (for blood moon). What other singletons might be handy?

I'm able to play with only 20 land, since I can do the combo with 2 lands, and go get it again with 3 (Congregation at Dawn). The Ageless Entity and Primal command are for longer games (I only have 2 of each).

I had one very satisfying game against a fully powered Stax deck where I used several StP and a Kavu to win, and another where I was 1 mana off casting the Seeds of Innocence in my hand and blowing him out 4 turns in a row (he kept destroying my land or increasing the cost of spells 1 every turn). Overall I'm having a blast playing it. Every person I show it to/play it against gets a kick out of it.

Wall of Shards is Perfect! Makes having a Predator on the board a bit more important.

Yes, that's the article (although I think I read more about a similar deck somewhere, maybe SCG). I'm going to add some Ageless Entities to the deck (maybe two) to make the late game a bit more viable. They should make the Lightning Helix's a bit better, and it allows you to target yourself with the Hero's Reunion once your early Predator has been dealt with.
I also run 2 Collapsing Borders, which is decent at slowly building up your Predators/Entities without making you a target.

I play R/G/w, and I haven't found the RR to be too difficult, but I have a lot of duals (both the good and bad ones). I only have 2 while spells: Primal Justice and Lightning helix, but I think that maybe at least 2 of the helix's should be StP, since it pumps your Predators.

I have 3 Worldly Tutors and 1 Primal Command, which I'd like to change to 2/2. The PC's are incredible late game, pumping your Predators or giving you life + searching out another creature.

The Lairs are really handy- I find myself hoping for them + 1/2 dual lands in my opening draw.

Invigorate is a great idea. I'll add those and the Creeping Mold (or maybe wasteland), as I found that Maze of Ith just wrecks me, as I usually only have 1 huge creature at a time, and I seldom want to extend for 2 for fear of sweepers in a large game. Sometimes I do put 2 out, just because 1 Primal Justice or Reunion can turn them into lethal damage.

I think what I'm still lacking is a way to get them back once they die, as they are always heavily targeted/swept, and I really only have a few really good creatures. Maybe Genesis or Eternal Witness- other suggestions?
The only other issue is flying creatures. I've thought about Decimate (decent in multi-player)

I've found this deck to be fairly weak 1-1, unless you get the Predator + pump and they get no creature kill, which is mainly luck. The 'each opponent' clause of the Cutter is what makes this deck shine (well, and negating the drawback of several other good spells).

Hull Breach is the best anti-artifact/enchantment card I've found, but I wouldn't mind something similar that gave life as well.

Fiery Justice is a essential card. I like to have 1 or 2 red cards that let me attack twice as well: Relentless Assault/Seize the Day.
I've tried using Lightning Helix and found it to be mediocre.

This deck has killed on the 3rd turn in a 4 player game, on the back of Skyshroud Cutter + Heroes' Reunion. There was a good article about it on MTG.com a while back as well.