I think it's possible to say that LeMans is in a different era now from what it used to be when Porsche raced there. (Don't quote me, I'm not an expert, I'm just throwing out some loud thoughts here
). If Porsche were to come back it would be under different regulations and rules for the cars in terms of structure and production. Hypothetically speaking, if the GT-One stayed on for the last year of its three year development cycle the chances are that it may have been successful and as such that would've carried over to the Bentley (for some reason I have it in mind that the Toyota team developing the GT-One was linked to Bentley... or is it Volkswagon and Audi... err, ignore me if I'm wrong). Which ultimately would have led to more competitiveness against the Audi R8s. Right enough, there's no faulting the Audi teams for pulling out all the stops in pursuing victory over the last few years.
For what it's worth, I think every fan would love to see a Porsche, Ferrari, Toyota, Audi, etc all lined up on the grid for a LeMans race. That would be a site to see.