1. How can oil "only" get so expensive? By oil, we are referring to the act of gathering existing oil. There is no limit to the cost of gathering. Going deeper and deeper, or from lower concentration will become more expensive as time goes on.
2. We have a lot of alternative sources of energy that put a lid on oil price. Can you explain the mechanism for this? Are you referring to the true cost of oil, or just at the fillup station? Are you saying the major cost of gathering oil is the input energy, and because the input energy is alternative, the EROIE is infinite? Please elaborate.
3. making artificial oil out of coal will become viable on a large scale. Making artificial oil has nothing to do with gathering oil. The reason they did that was that oil was a more valuable energy medium than coal, because it can be used for many products, not just trains/ships/electricity.
4. There's always nuclear power. I am a big fan of nuclear power, but have no faith in governments making a sound scientific analysis. So unless nuclear power becomes cheap (infrastructure-wise), I think peak oil is still a big concern.
5. Lot's of oil at sea we haven't explored. There's a reason we haven't explored it - it costs way, way, too much. But I'm sure we will as the EROIE goes down.