Isn't "[charconv] Primitive numeric conversions" a good fit for Clause 26 "Numerics library"?

I think so, too. Currently, it's hard to find. It makes more sense than [text], as text can represent more than just numbers.

Maybe put all of locale, regex. std::format under I/O-ish (because locale-using)

I'm not sure. You can use std::format while avoiding the locale-using overloads. I'd lean more to moving it to [text].

[meta] and [concepts] should be adjacent clauses, or [concepts] should become a subclass of [meta] adjacent to [type.traits].

I agree with making [concepts] a subclause. Not much point to a top-level [concepts] if new concepts are, rightfully, placed in more pertinent subclauses. Its title also needs to better reflect that "not all concepts are here!" Perhaps "basic concepts".

Is it time to move the container header synopses closer to where their contents are defined? E.g., [array.syn],[deque.syn],[forward.list.syn],[list.syn], and [vector.syn] are all adjacent at the top of the sequence containers subclause, [sequences], before we start on the definitions in [array] as a sibling node, and similarly for the associative containers, unordered containers, and container adapters. I don't think any other library clause collects header synopses in this way.

Yes, the containers structure is weird.