I've recently been looking hard at IMS and LTE - as both these technologies are finally gaining traction in the market place with Carriers upgrading their networks to 4G with VoLTE to follow very soon - within a year or so for many.
I've also been closely following the rapid rise of WebRTC and its deployment in browsers, Firefox and Google Chrome on you desktop now support WebRTC APIs and very soon it will be on your smartphone (http://googlechromereleases.blogspot.co.uk/2013/07/chrome-beta-for-android.html).
Carrier vendors such as Genband and others are all ready with their implementations of App servers capable of providing WebRTC.
More Interesting on this front as well is the recently announced Project Clearwater (http://www.projectclearwater.org/) IMS in the cloud.
It seems to me there is about a 1 year opening for the Over The Top providers (OTT) to get in on LTE and capitalise on the carrier's reluctance to use VoLTE. Its not to say there won't be issues - carrier's LTE implementations will probably be restricted to a single Data service offering for this first year, offering Dongles and WiFi Personal hotspots (MyFI) over a none QoS bearer service, which might not be the best for offering voice and video services (but that doesn't stop most of us using Skype!)
From the carriers perspective it might also be worth considering their position with respect to partnerships to enable OTT providers or deep packet inspection technologies to block the OTT vendors from utilising WebRTC applications. Partnership in my mind is better for both. It gives OTT providers the opportunity to get a QoS bearer service for their applications (QCI 5 and QCI 1 EPS Bearers) and potentially a custom APN to support this. For the Carriers innovation has not historically been a carrier's strength - partnership brings the opportunity to gain revenue from innovative services with little or no cost of development, and prevents them from the constant fear of becoming a bit-pipe provider only.
Whilst thinking about QoS/QoE it also struck me that its going to be a bit more tricky (not impossible) for 3rd party QoS/QoE software probes to monitor the Quality of Web RTC traffic, on two counts, 1) its peer to peer - unless forced to be otherwise (media anchoring); 2) the media and RTCP is "munged" (technical term) together into a single UDP stream to improve on the chances of successful NAT traversal. And on a third count - the media may also be encrypted.