I think it would make app development much more complex to have to find & use a midi stack, versus having midi devices well handled & a nice standard interface

I think it would make app development much more complex to have to find & use a midi stack, versus having midi devices well handled & a nice standard interface available. We could all be using user land networking stacks too over raw sockets but we don't do that either. Yeah, it too is simpler for the kernel. One of the key roles of the OS is to abstract access to resources. Turns out that's kind of useful.