I think that's more of a "soft" conflict. Nothing prevents you from using multiboot with kernel-power. Kernel-power is just a kernel, and obviosuly multiboot's task is to flash kernels, so they are inherently compatible.

(Multiboot only requires an initial kernel [LABEL HERE] able to run /sbin/preinit and the capability to flash a kernel like [GOTO HERE]).

Another issue is that Pali, and other people, don't like the fact that multiboot flashes a kernel every time you boot (or everytime you select a new kernel), because the number of writes to the raw NAND partition containing the kernel is limited.

Plus U-boot is much better and more elegant. But that's besides the point. In short: I would be strongly against adding dependencies or conflicts unless there's a real technical need for it.