802.11n is quickly becoming the de facto standard for commercially available WLAN equipment. The new technologies it introduced are very advanced, and it's unlikely that the full potential that 11n offers will be delivered to the market due to some practical limitations. However, the lessons learned from these limitations are quickly being addressed with new 802.11 specifications, most notably 802.11ac.
* 802.11p: WAVE -- Wireless Access for the Vehicular Environment (July 2010). 802.11p deals with data exchange between high-speed vehicles, and between vehicles and a yet-to-exist roadside WLAN infrastructure based on licensed spectrum in the 5.85-5.925GHz band. Activity in this area has been quite limited to date, as the overall implementation is complex, expensive and requires the appropriate business model if it's ever to see the light of day.
This specification provides a great example of how different specifications need to work in concert. Imagine driving down the freeway at 65 mph. Given the range of a typical access point is several hundred feet, your client will need to roam from one AP to the next every 5 seconds or so. The specific application of 11p can take advantage of certain techniques, like beamforming and increased power to perhaps extend the available range of each AP, but the amount of time spent connected to each AP will still be in the range of tens of seconds. [802.11p issues: "Will electronic toll systems become terrorist targets?"]
If a user is only going to be on an AP for approximately 15 seconds before being handed off to the next, the handoff time needs to be very short to provide a seamless user experience. Handoff is specifically addressed in 802.11r, also part of the 802.11-2012 roll-up, so it's imperative that the capabilities defined in both specifications be consistent and interoperable.
* 802.11r: Fast BSS Transition (2008). As more amendments have been added to 802.11, the time it takes to make a "transition" or "handoff" when moving from AP to AP has degraded significantly, causing problems for services like voice over Wi-Fi (VoFi). This amendment addresses this degradation, returning the handoff process to the simple 4-message exchange as originally designed.