A Lowell in Hunters Point with merit-base admission will still have the same demographics. Merit-based admission is what makes Lowell great, and as long as the school is great, parents will happily send their children there.
The problem runs deeper than where the school is, and getting rid of merit-based admission doesn't solve anything. The real solution is supporting under-privileged children and encouraging a culture of hard work and academic success among underrepresented minorities.