Are you using "seL4/Linux" in the style of "GNU/Linux"? Because then it should be "GNU/seL4" - that would describe an OS exposing the GNU core utilities on top of the seL4 kernel. There's no way to mix the Linux kernel with the seL4 kernel, other than using one to run VMs of the other.
It doesn't even have to be a Linux–compatible OS in theory although that is the standard to beat.
So its more of an economic argument than that of increasing security
A Linux VM isn't it.