In current develop branch as of September 28, add this to juce_VST3Headers.h in line 134 just below #include <public.sdk/source/common/memorystream.h> in the section guarded by JUCE_VST3HEADERS_INCLUDE_HEADERS_ONLY.
#include <public.sdk/source/vst/utility/vst2persistence.h>
Otherwise a VST3 plug-in will be unable to host other VST3. This pops up as No member named ‘tryVst2StateLoad’ in namespace ‘VST3’ at compile time.
