Want to add:
Grim Flayer
Null Rod
Dread Return
Beast Within
Vampiric Tutor (for Insidius Dreams)
Two fetches for the last duplicate forest and swamp.

Changes 10.01.2020
Current Average CMC: 2.00
    OUT --> IN
    Pernisious Deed --> Noose Constrictor
    Arbor Elf --> Boreal Druid
    Realms Uncharted --> Insidius Dreams
    Metamorphosis --> Arbor Elf
    Razaketh, the Foulblooded --> Tainted Pact
    Buried Alive --> Dismember
    Necromancy --> Plunge Into Darkness
    Animate Dead --> Spoils of the Vault
    Life Death --> Mindblade Render
    Phyrexian Delver --> Ad Nauseum
    Wayward Swordtooth --> Grafdigger's Cage
    Blast Zone --> Cabal Therapy
    Swamp --> Peat Bog
    Forest --> Hickory Woodlock

Changes 20.06.2019
Current Average CMC: 2.14
    OUT --> IN
    Cabal Therapy --> Veil of Summer
    Doom Whisperer --> Phyrexian Delver
    Lotus Cobra --> Shallow Grave
    Swano --> Collector Ouphe

Changes 15.05.2019
Current Average CMC: 2.16
    OUT --> IN
    Oppression --> Finale of Devastation (still testing this and don't have Finale)
    Fauna Shaman --> Survival of the Fittest
    Pit Bog --> Phyrexian Tower
    Hickory Woodlock --> Lake of the Dead
    Sunscorched Desert --> Blast Zone

Changes 22.04.2019
Current Average CMC: 2.16
    OUT --> IN
    Ad Nauseum --> Doom Whisperer
    Mindblade Render --> Underrealm Lich
    Gaea's Blessing --> Kozilek, Butcher of Truth
    Grafdigger's Cage --> Razaketh the Foulblooded
    Root Maze --> Reanimate
    Expedition Map --> LIfe / Death
    Traverse the Ulvenwald --> Buried Alive
    Arbor Elf --> Metamorphosis

Changes 11.04.2019
Current Average CMC: 1.81
    OUT --> IN
    Savage Summoning --> Necromancy
    Noose Constrictor --> Oppression
    Wild Growth --> Exploration/Wayward Swordtooth
    Sylvan Scrying --> Fauna Shaman
    Dismember --> Imp's Mischief
    Beast Within --> Caustic Caterpillar
    Swamp --> Rishadan Port
    Forest --> Emergence Zone

Changes 01.04.2019
Current Average CMC: 1.81
    OUT --> IN
    Ebony Charm --> Grafdigger's Cage
    Rifsweeper --> Root Maze
    Sickening Dreams --> Pernicious Deed
    Noxious Revival --> Cabal Therapy
    Scavenger Grounds --> Sunscorched Desert

Changes 04.03.2019
Current Average CMC: 1.80
    OUT --> IN
    Vampiric Tutor --> Mausoleum Secrets
    Graftdigger's Cage --> Ebony Charm
* No money, no problem

Changes 23.01.2019
Current Average CMC: 1.78
    OUT --> IN
    Deglamer --> Assassin's Trophy
    Trinisphere --> Beast Within
    Smuggler's Copter --> Mindblade Render
    Emerald Charm --> Duress
    Root Maze --> Noxious Revival
    Null Rod --> Expedition Map

Changes 27.06.2018
Current Average CMC: 1.80
    OUT --> IN
    Olivia's Dragoon --> Chain of Smog

Changes 11.06.2018
Current Average CMC: 1.80
    OUT --> IN
    Noxious Revival --> Null Rod
    Inquisition of Kozilek--> Graffdigger's Cage
    Thoughtseize --> Trinisphere
    Duress --> Emeral Charm (Ravnica 2 CMC Path to Exile but better)
    Expedition Map --> Dismember
    Seeds of Innocence --> Vampiric Tutor

Changes 05.06.2018.
Current average CMC: 1.70
    OUT --> IN
    Boreal Druid --> Wild Growth
    Beast Within --> Sickening Dreams
    Wayward Sabertooth --> Inquisition of Kozilek
    Doomsday --> Thoughtseize

Previous average CMC: 1.84

Sources/Primers:

http://tappedout.net/mtg-decks/gitrog-land-combo/

Future changes?:
    Double Titan:
        Gaea's Blessing --> Kozilek
        Ad Nauseum --> Doom Whisperer
        Riftsweeper --> Underrealm Lich
        Ebony Charm --> Unmask

        Sylvan Scrying --> Tainted Pact
        Forest --> Tainted Wood
        *Forest --> Forbidden Orchard/Hickory Woodlot
        Swamp --> Blooming Marsh/Cavern of Souls/Peat Bog/Ancient Tomb

Maybe:

Grafdiggers Cage
Thoughtseize
Emerald Charm
Silent Gravestone
Seeds of Innocense
Insidious Dreams

Toxic Deluge
Inquisition of Kozilek
Eldritch Evolution
Basalt Monolith
Boreal Druid
Collective Brutality
Grim Flayer
Doomsday

Prowling Serpopard
Dosan the Falling Leaf
City of Solitude
Planar Void

Vampiric Tutor
Mox Diamond
Mana Crypt