For a place that has been promised a comeback in recent years — only to see it never materialize — experts say Atlantic City is in uncharted yet promising territory that could help usher in a long-awaited recovery. Land prices are at their lowest in decades, local and regional developers with proven track records are investing in the city and the first credible nongaming project in years is under construction, with the potential to bring thousands of students and professionals to the Boardwalk as soon as next year.