The rundown on this is that CodeThink added Big Endian RISC-V because of a half-baked optimized networking scenario where somehow the harts (RISC-V speak for a cpu core) don't have Zbb byte manipulation instructions. Linus shuts down efforts made in mainline Kernel (!!) because these issues are extremely flimsy at best and don't have technical merit for complicating the kernel's RISC-V code and already extreme RISC-V fragmentation.

I've looked at more reasons that CodeThink came up with for Big Endian RISC-V, and trust me, that's the best that they have to present.