I can live with the core books for a while, but I would like to see modules/adventure paths released with some frequency and a strong digital focus such as apps like Morningstar, the return of Dragon/Dungeon in some worthwhile format, and better website functionality.
As player and DM...
Given how difficult it can be to find an Adventurer's League game due to poor group search and coordination tools on the D&D website or the lack of Encounters games with vacancies, putting too many eggs in this basket would be a particularly stupid thing to do.