Voor Vincent:
Their article makes many references to arbitrage-free pricing and risk-free valuation, quoting many academics in this area. Of course, quoting many names does not make the theory any more appropriate to use. Risk free, or more appropriately, risk-neutral valuation is indeed the foundation of a huge market of derivatives. However, the clue as to why this is not relevant is in the name, 'derivatives'.
Derivatives are products whose value is derived from other assets. A simple example is a forward contract and a more complicated one an option over an asset. Derivatives are valued using risk neutral, or arbitrage free, pricing because it is possible to create a perfectly replicating portfolio that will have the same payoff as the derivative from a portfolio of the underlying asset and cash. This means that no assumptions need to be made about the valuation of the underlying asset. Derivatives are about relative pricing. You wouldn't, for example, use risk-neutral valuation to determine the value of an equity or property.
The theories quoted are powerful but not relevant for valuing pension schemes. A pension benefit is an asset in its own right, not a derivative of another asset.
Wilbrink and Beenen would perhaps like to suggest that pension benefits are a derivative of risk-free investments. Indeed, they quote the example of a member having no risk tolerance and that the pension benefit should be treated as being risk free. They have ignored a big part of what a pension benefit is, though, when making this assertion.
However, I couldn't tell you how much above 100% the coverage was, as I don't know what the value of a pension benefit is. There is no market to tell me this, nor would it be desirable to have one. In fact, in the UK, we have specific legislation to prevent it. I could construct models to come up with a 'value' in the same way as I could value a company share or a property. It would only be a model, though, and highly subjective to my personal views. A market price would reflect everyone's view. For these reasons, talking about 'market value' of pension liabilities is a pretty pointless and unnecessary exercise.