The vendors outside Sheung Shui station still have placards offering one-card two-number SIMs. Don't know about pricing.
As to regular Mainland SIMs, the Chinese government is carrying though with its threat to cut-off unregistered cards. For China Mobile in Beijing, the cutoff was this week.
They've been doing that for years. My Unicom SIM obtained at the airport in January 2014 was cut off around March 2014.
Is it still possible to buy unregistered SIM cards at PEK, PVG, etc.? They always had people at a small kiosk near the PEK T3 exit who would sell you SIM cards (probably at tourist prices but you could get them for cash with no questions asked).