Linux has a large, large established user base at this point. If you want to attract people to a different platform, you need a compelling reason.
For people just looking to look/experiment/learn/play, 'something new' that's more easily understood because it's small might be enough, but that's unlikely to be a large user base.
On the IoT space it seems like not everyone is keen in having to deal with GPL and Linux, hence the myriad of FOSS MIT/Apache licensed OSSes that now exist.
Zephyr, NuttX, Mbed, Amazon RTOS, Redox, Tock...
And then there still the commercial alternatives.
The license is there for a reason, and its working.
As for "competitors", that's pretty cool :)
Which market segment does linux not totally dominate nowadays? Phones, big servers, embedded devices, HPC... Maybe you could argue desktops? Maybe? Still a very signficant player there however you dice it.
Going back to Linus' original email announcement then apply your framework and you don't predict linux competing anywhere let alone dominating everywhere. How could anyone? Smash Sun, IBM, HP all of them. No chance. None.
The future, it's really hard to predict except in hindsight.
Linux, (not big and professional like gnu), is not going to win but could find a niche somewhere. Hm, ok.