How does the PowerPC’s reverse bit numbering impact power consumption?

If you wire the bits as numbered to a conventional memory device designed with LSB as bit-0, the internal address bus will induce more switching from sequential access than normal. The internal row and column decoders will be working overtime consuming more power than necessary. Reversing the bus to deal with that isn't always straightforward on a space constrained board.

If I understand correctly, you are saying that with the reversed bit numbering, bit 31 (in a 32-bit address bus) changes most frequently with sequential accesses because it is the LSB but when wired to the MSB of SRAM, it causes switching in the column decoder for every single access.

That makes sense but I didn’t realize that it was difficult to simple swap the wiring. Are the physical pins ordered backwards as well (that is, do PowerPC’s A31 and A30 appear where A0 and A1, respectively, would be on a “normal” system)?

I have absolutely no idea why someone would connect the upper bits of the CPU address bus to the lower bits of the memory, if this is what the GP refers to. Their naming scheme seems irrelevant.

Almost all modern memory is built in a large matrix where the upper bits select the row into a buffer and the lower bits control a multiplexer that selects a slice of that row. Scanning incrementally through the memory will hit the fast multiplexer path and result in much faster access.

Propagating into the whole matrix at each increment is not only a power draw but a massive slowdown.

Since you have recently been through this, what were the other available options? There were a couple other rad hard processors under development years ago when I left the industry. Do you know what happened to those?