PBS has announced it is passing on funding a sequel to “Tales of the City,” but the story isn’t over yet. Some pubcasters, including WGBH in Boston, have started thinking about bypassing PBS altogether and backing a sequel series on their own.PBS and the BBC co-produced the miniseries based on Armistead Maupin’s stories of life among characters of various sexual orientations in ’70s San Francisco. PBS said it declined a sequel to the high-rated mini due to its funding cutbacks, but critics charged it backed away after stations in conservative parts of the country complained about gay and lesbian characters. WGBH — which produces series like “Masterpiece Theater” and “Nova” for PBS — has engaged in “hypothetical discussions” about initiating a “Tales” sequel with other stations, according to WGBH’s VP/station manager David Liroff. He cited as precedent the American showing of the Brit series “The Singing Detective,” which did not air on PBS but was acquired by several stations, including WGBH, for individual airings.