I guess this will just run into (probably justified) scepticism as a response but at least it can be said that Zuckerberg is strongly pitching that whatever Meta builds will be an open system. If you watch the last 5 mins of the keynote it is interesting because it ends with him almost begging developers to stick with Meta as the "android" of VR rather than opt into (what he is obviously referring to as) a closed Apple alternative.
Building an open system is what you do when you're small and you need 3rd parties to help you grow. If it's successful they'll do exactly what they did with Facebook. Do you know how I know this? It's pretty pointless for them to even say they're going to be open, because it's very well established how this goes at this point -the platform captures the value.
