After several days of tweeking, I have managed to make a fully functional multichannel reverb VST plugin. The plugin is developed in Juce and make use of frameworks from the IEM Ambisonic plugin suite. The reverb algorithm itself is the open-source freeverb implemented using Faust on a per-channel basis, with no reverb diffusing or leaking between channels.
More than anything else, this is a working proof-of-concept of how Faust can be used to develop VST plugins processing multichannel and ambisonic signals.