Curious: I'm not sure why a serious discussion of POW change is not on the table as a part of a longer-term roadmap.
Done right, a ramp down of reliance on SHA-256 and a ramp-up on some of the proven, np-complete graph-theoretic or polygon manipulation POW would keep Bitcoin in commodity hardware and out of the hands of centralized manufacturing for many years.
Clearly a level-playing field is critical to keeping centralization from being a "defining feature" of Bitcoin over the long term. I've heard the term "level playing field" bandied about quite a bit. And it seems to me that the risk of state actor control and botnet attacks is less than state-actor manipulation of specialized manufacturing of "SHA-256 forever" hardware. Indeed, the reliance on a fairly simple hash seems less and less likely a "feature" and more of a baggage.
Perhaps regular, high-consensus POW changes might even be *necessary* as a part of good maintenance of cryptocurrency in general. Killing the existing POW, and using an as-yet undefined, but deployment-bit ready POW field to flip-flop between the current and the "next one" every 8 years or or so, with a ramp down beginning in the 7th year.... A stub function that is guaranteed to fail unless a new consensus POW is selected within 7 years.
Something like that?
Haven't thought about it *that* much, but I think the network would respond well to a well known cutover date. This would enable rapid-response to quantum tech, or some other needed POW switch as well... because the mechanisms would be in-place and ready to switch as needed.
Lots of people seem to panic over POW changes as "irresponsible", but it's only irresponsible if done irresponsibly.