As rents rise across the city, Dudley Square seems to be drawing real estate developers who aim to attract tenants seeking the more moderate side of market rate housing. For Roxbury residents who have long clamored for greater diversity of housing and business in the area, this may signal the hoped-for change. ... But for Roxbury residents living in deeply affordable housing, the picture is bleaker. While rents on market rate apartments are currently near or below city average, they are climbing past the reach of the Section 8 tenants who have long inhabited the Dudley Square area; as a result, many of these tenants are likely to be displaced.