I doubt any normal hosts will enumerate a USB device without the USB 2 data lines. PD will definitely not work. You might be able to get an alt mode running.
They probably would enumerate just fine, because the SuperSpeed enumeration is completely independent from the USB 2.x enumeration. USB-PD uses a separate pin/wire, not the USB 2.x D-/D+ pair, and you cannot get an alt mode running (except the special analog audio and debug accessory modes) if USB-PD doesn't work, since alt mode enumeration goes on top of USB-PD.
I'd actually be interested in a 3-only cable. Force it to use high speed or bust, no surprises, no guessing at which proto runs under the hood on that "universal" connector. Didn't know it was possible; I might make one once I've got a spare cable (just today I've got another spare but they always have just 4 cables).
More for geeky/testing purposes than to replace all my cables, but still
