[Physicist]

But for "G" to be non-invariant with respect to direction, it would seem that there would have to be a corresponding anisotropy in the matter distribution of the Universe. But as far as I know, no such anisotropy has been observed.

It's not clear to me that an anisotropic G would lead to any anisotropy in the distribution of matter. But if it did, the matter distribution would have been used to set a limit on the anisotropy of G. Presumably this experiment was more sensitive than any existing limit, else it wouldn't have been mounted.

[longshadow]

It's not clear to me that an anisotropic G would lead to any anisotropy in the distribution of matter.

My thinking was that if the initial condition were an isotropic matter distribution AND an anisotropy for the gravitational constant, then one would expect over time that matter would preferentially cluster around the direction of maximum "G" value, thus resulting in a matter distribution anisotropy.

[Willie Green]

I have no problems retaining a belief that an ideal "G" is still a constant.
IMHO, they're merely misallocating gravitational effects of other gravitational bodies.
In the real world, an ideal "G" could never be measured because it is impossible to gravitationally isolate two bodies from the influence of other physical entities that exist in the universe.

Obviously, I'm no expert on the subject.
Just a humble engineer.
And when it comes right down to it, I've never had to use Newton's constant in roughly 30 years professional experience anyway.
So who gives a hoot what it is and what I think about it?

;^)