The Core plugin is actually not a plugin at all. It's built in to the Rack application itself, but you can add Core modules to your rack just like normal modules.
VST/AU support will be added with the "VCV Bridge" module in Rack v1.0, scheduled for release in December. Rack itself won't be a VST/AU plugin because of the major limitations of these formats, but instead you'll be able to connect Rack to your DAW by adding the lightweight VST/AU bridge plugin to as many DAW channels/tracks as you like, which will each connect an equal number of Bridge modules in Rack.
This cross-application method allows you to break the mindset of mixing linearly in your DAW and instead use nonlinear methods like cross-modulation between tracks, enveloping audio to control filters and sidechain compressors, etc. This "bridge" between applications is fault tolerant and doesn't matter which order you open the DAWs.