How are you defining "general-purpose OS"? Are you saying IoT and robotics shouldn't use a Linux kernel at all? Or just not your general purpose distros? I would be interested to hear more of your logic here, since it seems like using the same FOSS operating system across various uses provides a lot of value to everyone.
I think, that I want at least hard-real-time OS in any computer which can move physical objects. Linux kernel cannot be it: hard RTOS cannot have virtual memory (mapping walks is unpredictable in case of TLB miss) and many other mechanisms which are desired in desktop/server OS are ill-suited for RTOS.
Scheduler must be tuned differently, I/O must be done differently. It is not only «this process have RT priority, don't preempt it», it is design of whole kernel.
Better, this OS must be verified (as seL4). But I understand, that it is pipe dream. Heck, even RTOS is pipe dream.
About IoT: this word means nothing. Is connected TV IoT? I have no problems with Linux inside it. My lightbulb which can be turned on and off via ZigBee? Why do I need Linux here? My battery-powered weather station (because I cannot put 220v wiring in backyard)? Better no, I need as-low-power-as-possible solution.
To be honest, O think even using one kernel for different servers is technically wrong, because RDBMS, file server and computational node needs very different priories in kernel tuning too. I prefer network stack of FreeBSD, file server capabilities (native ZFS & Ko) of Solaris, transaction processing of Tandem/HPE NonStop OS and Wayland/GPU/Desktop support of Linux. But everything bar Linux is effectively dead. And Linux is only «good enough» in everything, mediocre.
I understand value of unification, but as engineer I'm sad.
