This will very likely affect JUCE. Here's a copy/paste of the email I received from Steinberg.
Dear VST Developers,
Steinberg Media Technologies today releases VST SDK 3.6.5, a maintenance
release for its VST SDK 3.6. Besides some issues that have been fixed with
regards to the included AudioUnit wrappers this update also includes new
VST interfaces, check below.
Here's a brief overview of changes :
Version 3.6.5 (2015/08/06)
New ChannelContext::IInfoListener interface: informing the Plug-in
about the channel in which it is instanciated (name, color...)
New IPrefetchableSupport interface: allowing a Plug-in to inform the
host that it does not support prefetch/ASIO Guard (could be dynamically)
New IUnitHandler2 interface: allowing a Plug-in to inform the host
that an assignment Unit-Bus defined by IUnitInfo::getUnitByBus has changed
New IAutomationState interface: informing the Plug-in about its
current automation state
use "#pragma once" instead of "#ifndef"
New VST 3 Plug-in ChannelContext showing how
ChannelContext::IInfoListener interface is working
New VST 3 Plug-in PrefetchableSupport showing how
IPrefetchableSupport interface is working
"VST3 Host Checker" Plug-in updated with new checks
support MIDI output
fix crash with namespace conflict with Mac OS X 10.10
add PresetAttributes::StateType support in
New predefined 3D Speaker Arrangements: k91Atmos
add some new unit tests: Bypass parameter support is mandatory for
FX Plug-in (not Instrument)!