At the last GPA meeting, a BART rep said there are no plans for development on the lot in the near the future. As the fabulous Bonnee Waldstein wrote in her thorough notes:
Tim Chan, the station planner for the Daly City to Powell Street stations, addressed the local situation at the Glen Park station. There are no plans for development of the BART lot on the drawing board for the near future.
However, the lot will be used for construction staging and we will have seven possible weekend closures of Glen Park BART between July and October. They will be working on the rails and problematic track curves between Daly City and Glen Park. There will be a media blast several weeks in advance when the schedule is set.
For the full notes, see this earlier post.