DCA-PHL is also a short flight distance-wise (just 40 miles longer):
http://gc.kls2.com/cgi-bin/gc?PATH=d...OR=&MAP-STYLE=
And, it doesn't face any "climb to 15k feet in the first 10 miles" rules... or a handoff between one country's ATC and another's. Yet, it's also blocked at ~1 hour.
My hope for the future is that China and HK effectively eliminate their border. While this would annoy many Hongkies, it's no secret that one of HK's main purposes these days is to support development in the PRC; even with echannels, enormous amounts of our time are wasted at border crossings. If they open the border, a direct train between HKIA and Shenzhen/Guangzhou would become extremely viable -- just extend the AEX across Shenzhen Bay (I'm getting tired of taking those vans every time I fly into HKG, but need to get elsewhere in the PRD).