It's just too much development work at this stage - not only the VST integration itself, but building a full MIDI sequencer timeline, editor, etc to support instruments.
Other DAWs do this perfectly well so I'm focusing on the 3D virtual environment moreso than tradtional DAW functions. Audiocube isn't a tool to compete with the likes of Ableton and Logic, but something to run on the side.
Although, if I had a big enough team I would love to give it all of these features. I'm just doing it solo at the moment, so I need to have a narrower focus.