Remember, the big news is the Rack Extensions. It’s the only way forward on future platforms like iOS. Even with cross-app audio APIs, providing curated plugins (rather than manually added ones) seems to be the ideal way to provide add-ons for your audio software in the new sandboxed era of computing.
Who else is ready?
Ableton: Max for Live could conceivably become their version of an “internal” add-on store.
FL Studio: Synthmaker patches could serve this purpose as well.
Logic: Apple can use the architecture from GarageBand lessons to provide add-ons within the app (you could say the “jam packs” are a precedent as well).
Pro Tools: *cricket, cricket*