I wish there was a reasonably speced out microkernel OS that, if not gaining traction, wasn't based in conspiracy theory or academia but in the practical benefits of having it.

I see a very beautiful world where a small kernel could handle preemptive scheduling, virtual memory, and provide a virtual file system and virtual socket abstraction. Devices could use the socket layer and file system to take control of DMI devices provided by the firmware, but still run in userspace. If you used the plan9 "everything is a file" model, system devices could easily exist in their own directory, etc.

Then you use a newer privilege model, where an application derives its rights from its parent, who can either down-cast their rights or keep them at the same level as the parent, and the privileges influence the application specific view of the file system (like in Plan9).

For IPC, I'd really want to put in an effort to use the lower range ipv6 addresses in a highly optimized virtual socket dispatch so you could have one protocol to rule them all. Every IPC and remote communication, to any device, to any service on any machine, could be done over an abstracted ipv6 layer. Screw the maligned utility of dbus, unix sockets, RPCs, etc, use what you already have and optimize the hell out of that.

Also, I'd like to see a reasonable and sane file system. I like how /usr in Unix has nothing to do with a user anymore. How some systems expect /cdrom to be a thing in an era where a tremendously small fraction of machines have baked in CD roms, and those would be SATA devices if not USB externals. The Linux and OSX top level file systems always drive me nuts.

I'd use that visibility privilege model to have multiple users - an all user, public user, root user. System binaries would be under root, users would have visibility on themselves and any other user they are given access rights to (passworded or not) including the all and public. You can install and compartmentalize binaries and libraries appropriately. If you want a jail, create a user without any access privilges on other users, and they can only run in a personal vacuum. If you do a good security model where only applications within +/-1 of the privilge heirarchy can see in the socket layer another process, a jailed user would only have visibility on servers like what we have in pulseaudio and X instead of hardware like the gpu or alsa, and those services could be steeled against aggressive input.

Such a system I feel would be a breath of fresh air for writing applications. If the runlevels were something like:

0: kernel
1: hardware devices and init
2: hardware service servers, daemons, and login manager
3: max privilge user session, possibly more login managers and daemons to support lower privileged users.
4..n: restricted user sessions with limited views of other contexts.

Any layer could explicitly passthrough a higher level service or daemon to visibility on the lower tiers, but it would need to be explicit, you have a very limited scope by default.

I'd love to write software in a context like this. Security sounds better to me, communication is unified, and what you see (in the filesystem) is what you get.