EDIT: Still reading the articles. Gernot reminds me PikeOS from Sysgo was "a L4 clone." They got acquired by Thales after quite a few iterations on their PikeOS product. An annual report I found by Thales said they were acquired for over 20 million Euros. Still on low-end in terms of market value but might have been successful depending on money in vs gained.
EDIT 2: Read his blog posts. Before OK Labs Post No 6, here's what he claims about L4 uptake:
"Secondly, a lot of stuff is running on L4: – Qualcomm modem chips have been running our L4-embedded kernel since 2006, that’s a few billion devices – The security processor of all iOS devices is running a modified version of our L4-embedded, that’s another 200-300 million devices every year – seL4 is being deployed on autonomous military air and ground vehicles, with the first autonomous helicopter flight in July 2015 – many other safety- and security-critical deployments are in progress.
I’m not aware of any real-world deployments of Minix."
Of course, we found out later Minix 3 was in Intel's baseband. So, there's two of them with people claiming massive deployments in supporting CPU's/MCU's. What you alluded to didn't refute a large number of units. Just that the company was anything as good as marketing presented. It wasn't. A few deliverables kept selling, though, per same source. He was wrong about Minix 3, too. Probably because it was Intel's secret for a while. I bet they wanted the reliability, included apps/code, and BSD license.