As for the 17th-century gateway ancestor with the longest matriline, that distinction would seem to be held by Anne (Humphrey) Palmes, which is not surprising given the nearness of her noble ancestors:
Maud d'Avranches = William de Curcy
Hawise de Curci = Renaud de Courtenay
Egeline de Courtenay = Gilbert 'II' Basset
Eustachia Basset = Richard de Camville
Idonea de Camville = William Longspee [grandson of Henry I]
Ida Longespee = Walter FitzRobert
Ela FitzWalter = William de Odingsells
Ida de Odingsells = Roger de Herdeburgh
Ela de Herdeburgh = William le Botiler
Ankaret le Botiler = John le Strange
Eleanor le Strange = Reginald de Grey
Edith/Ida de Grey = John Cockayne
Elizabeth Cockayne = Lawrence Cheyne
Elizabeth Cheyne = Frederick Tilney
Elizabeth Tilney = Thomas Howard
Elizabeh Howard = Thomas Boleyn
Mary Boleyn = William Carey [officially; perhaps Henry VIII]
Catherine Carey = Francis Knollys
Anne Knollys = Thomas West
Elizabeth West = Herbert Pelham
Elizabeth Pelham = John Humphrey
Anne Humphrey = William Palmes [to Salem, MA]
Anne (Humphrey) Palmes also has modern matrilineal descendants, for instance:
Susan Palmes = Samuel Avery
Mary Avery = William Walworth
Rebecca Walworth = James Packer
Zurvier Packer = Joseph Sherphardson
Salome Shephardson = Walter Bell
Eliza Ann Bell = Horace Kemp
Ida Grace Kemp = Charles Dewey Miner
Mavie Lucretia Miner = Thomas White
Bell Marion White = Edward Galvin
Nancy Galvin = Kevin Murphy
Dana Murphy [residing in Oakland CA as of the 2012 obituary of her mother] [33 generations in total]
One prominent collateral descendant of this matriline is Charles Cavendish-Bentnick, great-grandfather of Elizabeth Bowes-Lyon, the late Queen Mother:
Catherine Carey = Francis Knollys
Lettice Knollys = Walter Devereux
Penelope Devereux = Thomas Rich
Essex Rich = Thomas Cheke
Anne Cheke = Robert Rich
Essex Rich = Daniel Finch
Mary Finch = William Saville
Dorothy Saville = Richard Boyle
Charlotte Boyle = William Cavendish
Dorothy Cavendish = William Cavendish-Bentnick
Charles Cavendish-Bentnick