Three significant benefits that we see in the emerging 802.11ah that might give it an overall edge against the others are:
1) Wi-Fi alliance is very mature in supporting and reassuring the interoperability between 802.11 gear. We believe 802.11ah will not be an exception
2) 802.11 has a very stong brand and great acceptance by the consumers
3) It's built upon a very mature and successful technology (11ah PHY layer inherits the advancements of 802.11ac, such as 256QAM)
I'm not familar with Z-Wave, so I only compare 802.15.4 and 802.11ah.
802.15.4 (Zigbee) is established technology, more than 10 years of market experience. Although it is not hugely successful as Zigbee standard, but 802.15.4 radio is quite popular as as low-cost low-power radio platform for industry use. Several radio-integrated single chip LSIs solutions are already in market, they are cheap and very power efficient.
One drawback of 802.15.4 is it is not designed to run TCP/IP. Though it is surely possible, but not very popular yet to date. I'm not quite sure if it is good idea to implement TCP/IP on every end nodes, or left device link as propriately while providing Internet uplink at the gateway (access point / router).
The strength of 802.11ah is it is designed to run TCP/IP, so existing IP-based applications can immeditely run on it. It is just another variety of familiar WiFi, with more range but less throughput. Existing WiFi security solutions such as WPA, WPS, 802.1X should be able to used on 802.11ah. Even though both 802.15.4 and 802.11i security are based on same 128-bit AES, 802.11 offers more flexible and powerful key management methods.
The major drawback of 802.11ah is (of course) late starter, no LSI is available yet. Even if earliest radio chip may be available in 2014 (I think it is too optimistic), it will require some years to catch up 802.15.4 for integrated single chip LSI. It should consume some more power than 802.15.4, due to more complex modulation scheme (DSSS vs OFDM).
802.15.4 at 915MHz band uses 40Kbps BPSK modulation with 600Kcps spreading code, resulting 40Kbps throughput in 1.2MHz channel bandwidth. 802.11ah uses BPSK modulation in 40usec symbol interval (25symbol/sec) x 24 data-subcarrier OFDM, 600Kbps raw throughput is redundent by 1/2FEC and 2-rep (sending same data twice), resulting 150Kbps throughput in 1MHz channel bandwidth. They are very different technologies but quite competitive (I think) performance.
So key question is "Do you wait for IP-capable low-power radio (802.11ah) or will adopt existing low-power non-IP radio (802.15.4)"? If IoT/IoE market is really ermerging and want immediate "last 100feet" solution, 802.15.4 will have the edge being ready. If they can wait 1-2 years, eventually 802.11ah may gain advantage. This is my observation over two technologies.
"...across a distance at least 50% longer than today's .11n consumer devices."
Sorry, I am not aware about the distance supported for .11n standard...but I believe .11n works in the 2.4GHz - 5GHz frequecy band? What is the distance supported for .11n and what it would be for .11ah?