The title is accurate, though. The use of PCIe is exploding everywhere, but we're putting it in every other interface and the "PCIe expansion card" connector and form factor is seeing relatively less use overall.
Because everything is standardizing. You don't need ports for TV tuners or proprietary camera memory cards anymore. Everything you do need is now built in to the mobo.
It's not 'dead' at all, that's what I was referring to. It's not going anywhere either for the remaining usecases.