Doesn't Haiku have the same limitation that AROS has in regards to drivers? I assume you'd want to support a limited set of architecture first, but wouldn't the ideal be to ultimately support as broad a range of hardware as possible? Am I missing something here?
Haiku can use all of BeOS's drivers, but also includes a source level BSD compatibility layer to allow for network drivers to be recompiled and dropped in.
However, as with AROS, some Haiku forks are looking to include gallium3d as a means to boost hardware compatibility whilst reducing developer overhead.