Why compare copyright to land in the first place? To compare one special case to another special case implies that they are/should be special in the same way.
As far as I can tell copyright has ended up being similar to ownership of normal PP where the property in question will eventually wear out, break down or be otherwise lost. Adding a life term even replicates the fact that we don't usually know how long the property will last
And I think that a perpetual copyright might benefit those wealthy enough to buy up large number of old copyrights on speculation and aggressively pursue scofflaws but unlikely to provide much benefit to the heirs of the average creator's heir.
I also think that a law so definitively opposed to the cultural practices of most of humanity would in the end be as successful as prohibition.
