Think about it from Apple's perspective. How much does the iPhone app store make for them? How much does software on the Mac make for them? All software that is ever installed on a Mac, what is their cut. What would you do? Of course it's going to be locked down like an iPhone.

It will be like iPhone.

Unless the EU forces Apple to do it differently.

The apple device it seems most like is the iPad and likely iPad with sidecar.

The presentation clearly showed that you could use the goggles to display your macbook screen, so in that sense, if you want a screen in 3d space, or maybe even multiple screens in 3d space, you can have a window to whatever your macbook can do.

In the presentation, I believe they showed that they abstracted away the parts of IOS that are common to all systems and built visionOS on top of it, so we are likely to see a locked down IOS like ecosystem.

The flipside is that AR is an unproven technology with no killer apps, so a closed ecosystem and limiting OS api access could stymie innovation that might validate their investment in unproven "future tech."

I think it is plausible that apple might let a steam like service on their platform.

I think it will be locked down and they will have a very beneficial offer for developers in order to lock them down too. VR/AR doesn't have killer apps yet, developer's ideas will decide who wins the race.