The sector of downtown that seems to make the most sense for an "urban" Target and/or a grocery store (or Trader Joe's) is the
Green redevelopment. In its favor are a clean slate site, proximity to many of the existing (and coming) condos, and good accessibility via Cesar Chavez for those who visit by car.
Seems reasonable to think that Trammell Crow will explore all the "big retail" possibilities to fill a niche with their Green master plan. Even though such a store was explicitly mentioned in only one of the competing Green proposals, and it wasn't TC's, that hypothetical H-E-B did seem to capture the imagination of a lot of people.