"What kinds of machines can and cannot be conscious?"
We know brains can be, but how?
What are their relevant properties
(if their weight, for example, is not)?
If we pare down the properties of the brain
to test which ones are and are not needed to be conscious:
What will our test be?
We are right back to Turing-testing again,
the only non-telepathic methodology available to us,
because of the other-minds problem.