Of people with an interest in the case, I am sure that there are ardent sceptics and ardent supporters that do not consider all possibilities Rob. Some people in the middle ground will do but what percentage of the total?
I have a feeling the tide is turning in favour of the Replacement Child theory (RC theory). I haven't read his most recent book but doesn't Danny Collins advocate this RC theory.
I'm not sure if Goncalo Amaral ever thought it was a possibility, in fact I think he may have had some idea of something going on that was larger than just a dysfunctional family, when he talks of the secret services being involved.
Richard D Hall in one of his videos brought up an email with information that suggested the Interpol officers had been and gone before the GNR turned up.
The McCanns have at times suggested such an outcome as the RC theory.
Even I can't really believe it myself, but it was the only solution that seems to not run up against a brick wall.
I've looked for the reason it fails and I haven't found it yet.