The
Dead Reckoning +
Shadowborn Demon combo is definitely worth it.
Although I personally think that completely dropping
Treasured Find is a bad idea.
My Abzan Seance deck runs similarly to this. With a stupid amount of recursion (3x Reckoning, 2x Treasured Find, 2x Seance, 1x Gravedigger).
I actually think Dead Reckoning really wants to have
Treasured Find along side it in a deck like this. Yeah, most of the time you are bringing creatures back with Treasured Find, so Reckoning is doing the same thing for you (albeit slower) AND providing you with removal.
Decks like this though generally tend to be light on removal though (to make room for their value creatures/engine cards) and in this case
Treasured Find fills that roll quite nicely. Treasured Find not only gives you another means of pulling those big ETB fatties out of the yard, but also gives you a reliable way to recycle Dead Reckoning itself. Treasured Find is recursion for your creatures when you need it to be (which will be most of the time), but will also allow you to do stuff like bring back Reckoning after you have used it and/or pull it back from the yard in those scenarios where your self-mill decides to fill the yard with all your removal cards.
I actually had a game once where I killed an opponents entire HAND worth of creatures with the single copy of
Shadowborn Demon and all the recursions effects. Cast Shadowborn, kill opponents creature. Next turn sac Shadowborn to itself, Reckoning to kill another creature and put Shadowborn on the top of the deck. Next turn draw Shadowborn, cast it, killing another creature. Next turn sac Shadowborn to itself, cast Treasured Find to bring Reckoning Back, cast Reckoning to kill creature and put Shadowborn on the top. Next turn draw Shadowborn, cast Shadowborn killing opponents creature. Next turn sac Shadowborn to itself, cast Seance, at opponents untap bring Shadowborn back with Seance killing another one of their creatures.
^^This sort of thing happens more often than you might expect in my Abzan Seance deck, I could see it working in a deck like this as well.