It's not going to happen tomorrow, but MTA is strongly considering closing some subway station entrances to prevent overcrowding on platforms. According to spokesman Adam Lisberg, there's "zero risk" of these entrances being closed in the near future, but unless they come up with money to drastically redesign passageways and stairwells, some stations may be shut down to ease congestion during peak periods.
MTA says that they need between $340 and $465 million to make alterations to the Grand Central Station exits located at Fifth Avenue and East 51st Street by 2030. That money is supposed to be funded by the rezoning of Midtown East, but that may not come fast enough.
Again, there's no need to panic in the interim, just be aware of what the future could hold.