New Skaro was, presumably, the new homeworld of the Daleks, established by the 26th century when Ace was in Spacefleet. (PROSE: Birthright)
Working with the Reborn Master, the Dalek Time Controller created an alternate timeline where it took over Earth from Paris in 1921. By 1961, the planet was "New Skaro" and converting the bio-matter of humans, Sontarans, Draconians and other aliens into a New Dalek Paradigm. (AUDIO: Master of the Daleks)
The Cult of Skaro later planned to turn Earth in 1930 into "New Skaro". (TV: Daleks in Manhattan/Evolution of the Daleks)