Update 12.11.2015: Today on the World Magic Cup stream, both Wastes and Kozilek, the Great Distortion were confirmed.

Ian Duke also discussed some of the rules surrounding these new cards. The symbol in the casting cost of Kozilek, the Great Distortion represents colorless mana and must be paid for with colorless. The 8 can be paid with mana of any color OR colorless mana (known as generic mana). The symbol will now be used to indicate colorless mana production and costs that can only be paid with colorless mana. Duke noted that Kozilek's Channeler produces two colorless mana, indicating older cards have not had their function changed.

Wastes are a Basic Land with no type, meaning a copy can be retrieved with Rampant Growth but does not count towards Domain on Tribal Flames. Wastes will appear in boosters of Oath of the Gatewatch at a higher rate than usual, as the only Wastes you will be able to play with in Limited are those you draft (similar to the Snow-Covered Lands) from Coldsnap.

Update 11.18.2015: Images from the original Twitter posts have been removed. The unconfirmed spoilers are featured below:

Earlier today Twitter started to stir with potential leaks from the upcoming set Oath of the Gatewatch. Images appeared on two accounts the contained unconfirmed cards from the next release. If real, these cards signal a huge change is coming to Magic.

The first tweet appeared from the MTGFocus account:

The second from user george_gone which pointed to a thread from MTGSalvation as the source of the potential cards:

If real these cards show that Oath of the Gatewatch will introduce some sort of colorless mana. The long awaited and often rumored "Barry's Land" - a Basic Land that produces colorless mana- may have finally arrived.

Update: According to this clip from PAX Australia 2014, "Barry's Land" is technically possible within the rules. Foreshadowing?