Now that JUCE_COREGRAPHICS_DRAW_ASYNC is no longer meaningful, I think it would beneficial to give a warning during compilation if it is found to be defined in a project, to give the developer an heads up in case they missed the BREAKING-CHANGES doc.
In general, I think it would be good practise to give such warning for every macro when it is no longer used by JUCE. That would give us developers a chance to clean up our #defines with increased confidence.
(Same idea already mentioned here: Ouch! kAudioUnitParameterFlag_IsHighResolution problem, fix needed! - #3 by yfede)