I see, thank you! That also seemingly explains why -2 wasn’t used… -2 was taken by this other proposed stateful precompile. 
(And I can imagine that -1 wasn’t used for other reasons.) Although going by below sounds like these are being moved to low addresses regardless.
I do have to say I don’t really understand the distinction being drawn, though. One way or another, you need this list to be stored somewhere. I don’t understand why it makes a difference whether it is stored somewhere available to an opcode, or stored somewhere avialable to a precompile.
Like, you say “right now you need the execution state and some additional context”, but that statement depends on defining “execution state” in a particular way, right? I would have just said that, because this list is accessible, that makes it part of the execution state. Evidently “execution state” has some technical meaning here that excludes this sort of thing, but even granting that, why does it make a difference? Why is the line that is being drawn a useful line to draw, such that doing it the precompile way is easier than doing it the opcode way? To me it just seems like they both require storing this information – which I would have called state information, though I suppose it doesn’t fall under what is technically being called state – somewhere, and it’s not clear why opcode vs precompile makes a difference…