I believe that as we continue to add users to the system by scaling capacity that we will see more new nodes appear, but I'm at a bit of a loss as to how to empirically prove it.
I do see your point on increasing load on archival nodes, but the majority of that load is going to come from new nodes coming online, they're the only ones going after very old blocks. I could see that as a potential attack vector, overwhelm the archival nodes by spinning up new nodes constantly, therefore making it difficult for a "real" new node to get up to speed in a reasonable amount of time.
Perhaps the answer there would be a way to pay an archival node a small amount of bitcoin in order to retrieve blocks older than a certain cutoff? Include an IP address for the node asking for the data as metadata in the transaction... Archival nodes could set and publish their own policy, let the market decide what those older blocks are worth. Would also help to incentivize running archival node, which we do need. Of course, this isn't very user friendly.
We can take this to bitcoin-discuss, if we're getting too far off topic.
Pruned nodes are not the default configuration, if it was the default configuration then I think you would see far more users running a pruned node.
But that would also substantially increase the burden on archive nodes.
Further discussion about disk space requirements should be taken to another thread.
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