How would you like an art gallery in downtown Southborough? What about a playhouse? Or more restaurants and shops? The Zoning Advisory Committee (ZAC) believes enabling that type of development downtown — as well as in Southborough’s other three villages — is key to reinvigorating the village district. But some downtown residents feel the specific zoning changes proposed by the ZAC will threaten the historic character of the village districts, and they plan to share their concerns at a public hearing on the matter tomorrow night.