> But if libc will be developed in tandem with kernel... the "mere
> aggreggation" defense evaporates
I don't believe you're correct here.
First, the "mere aggregation" clause is not a "get out of jail free" card, where any cross-derivation of two different pieces of software magically becomes just fine if they're aggregated together on a single CD. If two works are legally derived, then you have to deal with the GPL, REGARDLESS of whether they're aggregated or not. The "mere aggregation" clause just makes crystal clear something that is probably already true anyway: that bundling two completely unconnected things together on a single media does not magically make them legally derived from each other.
Second, the reason glibc, etc. and the kernel are allowed to use different licenses is not the "merge aggregation" clause. These are not considered to be derived works of the kernel and so they don't have to take the kernel's license into account.
So whether libc is developed by the kernel developers or by GNU, and how they are bundled (or not) together, is not relevant in terms of licensing. All that matters is derivation (without derivation there is no way to enforce) and the content of the license.