The Winthrop Society is a lineage group for descendants of the early Massachusetts Bay Colony settlers (as opposed to Plymouth Colony, which consisted of Cape Cod and modern-day Plymouth and Bristol Counties - roughly - plus some disputed areas of Rhode Island. There is a map on wikipedia under "Plymouth Colony" showing the line of demarcation.) The Society is named for Massachusetts Bay Colony governor, John Winthrop, he of "city upon a hill" fame. Winthrop led the first fleet of ships that brought Puritan settlers from England to what is now Boston and environs. There is no complete list of settlers who arrived in the Winthrop Fleet or the many ships that came to the Colony over the next few years bringing Nonconformist English settlers. (Nonconformists were Protestants who did not wish to conform to the state religion, the Church of England.) The process of joining the Winthrop Society, like other historical lineage societies, helps people learn their personal family history and in the process learn American, European, even World history at the micro level vs. the macro level (kings, presidents, wars, political movements (Reconstruction) large-scale social events (the Great Depression), etc.) typically taught in schools.
The Winthrop Society's stated intent is to compile (eventually) a complete list of settlers, make up a bibliography of relevant books, to identify the English origins of each settler or family group, to create a database with this information, and to publish their findings in their quarterly newsletter. To my knowledge, that last item is the only thing they actually do, but it's something. Perhaps by being more inclusive the Winthrop Society can achieve the size and resources of its neighboring group to the south, the Mayflower Society, and like them publish more substantive original scholarly works. If the vote in April favors the motion it would be a step in that direction.