Apple had previously announced that developers of new apps must support 64-bit architectures (to take full advantage of the A7 and A8 technology) by February 1st, 2015. Today, Apple has reminded developers of this deadline as well as clarifying the situation for existing apps.
Updates to existing apps must be made 64-bit compatible by June 1, 2015. After that date, any submissions of only 32-bit apps will be rejected by App Review. The process for updating apps to support 64-bit architectures is not trivial, but it is not particularly difficult either. Therefore, these rules shouldn’t be seen as punitive — Apple is just nudging the developer community forward.