Okay, sorry! Still a long way to go before the idea becomes sufficiently well-specified to make much sense to me though. Perhaps an examination of yacy could provide you a concrete example of the ways in which such things are complicated. One would need to do much better to end up with a suitable replacement for the ways many of us use searx.
It was wanting to use ActivityPub and the "I fail to see any downside" which led me to read the rest of your post in a way that might've been overly pessimistic about its merits.