The intention is to have a stable driver abi which should allow you to build an arbitrary OS on top (fuchsia itself is exceptionally modular and doesn't have a lot of opinions it imposes on products built above it). Of course similar to a Linux BSP not helping Fuchsia run, such a layer wouldn't enable you to run other OS on top that are not built on top of fuchsia. There is also a limit to what you can generalize in the OS layers as some products may implement private apis between themselves and specific hardware drivers. A stable ABI also implies that the drivers won't necessarily need to be open source, but if the goal is to keep the rest of the OS updatable even if drivers themselves are not updated, that is a necessary concession. There are also many other practical benefits to keeping drivers open source regardless of license obligations to do so. That all said I'm very optimistic about this direction regardless of these caveats.