We're using seL4cp. I have written simple timer drivers for the Odroid-C2 and imx8mm platforms. Neither of these platforms is officially supported by seL4cp at this time. The former requires support for edge-triggered interrupts in seL4cp and the latter a more recent version of seL4. We have a combination of TFTPboot and Internet-enabled power switches to load and to run the binaries.
Alain