Great insight Rob, thanks. I too wish Shimano would sell hubs in a wider variety of drillings. But I guess in their mind that would compete with their housebrand wheels too much. Sad to see the two titans of traditional wheelbuilding (Shimano and Mavic) refuse to keep up with the times to sell more proprietary wheelsets. However, 32h and 3x lacing with a modern stout v-section rim is still the way to go for people who consider strength and durability to be the most important thing for a wheel.
It is sad. More and more traditionally parts only manufacturers are moving to prebuilt only. About 3 years back I was in the Mavic booth and talking to a rep. I asked about rims and their poor availability in the US. I was hoping there was a solution like going direct. He simply said that it was their specific intention to slowly phase completely out of the rim only market all together. It just isn't where their focus is anymore. He then shifted gears to talk about carrying the prebuilt line.
Alas - I don't think the consumer is losing out. There are still plenty of us who will build in the margins.