Yeah, I really want to see an Mlp version of this Slender Series.

And I have a pretty good idea on which ponies should be the Collective.

Yes!
TribeTwelve!
The best Slenderverse series of all 3!
Although there had already been a good bunch of ponified versions of the Collective on Deviantart.

Observer

Firebrand

DeadHead

Swain

Cursor

Mr. Scars

Persolus

All hail our Keeper!

4538808 I was actually thinking that the Mane Six and Spike could be come the Collective.

4538999 That could work as well. However, I still think there should be others, who are already Collective members.

4539653 Hmm... Whoever they might be maybe up to you.