In article , "Richard D. Saam"
writes:

This assumes neutral hydrogen in gas form.
What if the neutral hydrogen were in aggregate or clumped form?

One can argue that such neutral hydrogen aggregates
would have to be extremely cold (2.7K) to form
and the present BBN models "baryon budget" do not allow them
beyond the 4.9% ionized form
but the fact is that current analytical methods
(other than gravitational lensing methods)
cannot detect them if they exist.

This sounds to me like Russell's teapot or back issues of the ApJ as
dark matter. Unless you have a convincing reason why something should
exist (he how they can be so cold), saying "we can't (yet) rule it
out observationally" doesn't make a very strong case.