This plugin uses parts of the SpectMorph API that are no longer supported in the upcoming SpectMorph 0.5.0 and above.
In 0.4.x, the host can
manage polyphonic instantiation itself, which this BEAST plugin does, i.e. for a track with 16 voices, there are 16 MorphPlanVoice instances, each host voice corresponds to one internal SpectMorph voice - the host interprets note-on/note-off and renders voices
leave it to SpectMorph and just send note-on and note-off events using SpectMorph's MidiSynth
The instrument editor / WavSource operator introduced in SpectMorph 0.5.0 requires that the voice management is done by SpectMorph, which is what SpectMorph smjack, VST and LV2 have always done. This means that using SpectMorph inside BEAST's modular synthesis engine is no longer possible. With 0.4.x you could add a BEAST filter with BEAST ADSR after the SpectMorph plugin, and it would be done per voice. With 0.5.x this is no longer possible.
So I'd recommend that we don't merge this as-is, because it would allow creating sounds that would no longer be supported by newer SpectMorph (>= 0.5.0). Instead, once we have some kind of Device API, the BEAST-SpectMorph plugin should use it. This would also repair the "Portamento Mono" mode SpectMorph has, which depends on having the midi notes available.