>A mandated singular public cache has potential slippery slopes.
That may be, but it seems like everything has a slippery slope - if the wrong person gets into power, or if the public look the other way/complacence/ignorance/indifference, etc, etc. It shouldn't stop us evaluating choices on their merits, and there is a lot of merit to entrusting 'core infrastructure' type entities to the government - or at-least having an option.
This is an argument against centralization more than it is against government.
"One index to rule them all" seems more fraught with difficulty than, "large cloud providers are unhappy that crawlers on the open web are crawling the open web".
If the impact stopped at "large cloud providers" being unhappy, I think that you're correct. But I think we've seen considerably downstream "difficulty" for the rest of society from search essentially being consolidated into one private actor.
A mandated singular public cache has potential slippery slopes.