David Airlie has been working on Multi-Stream Transport support for effectively daisy-chaining multiple DisplayPort connections, as needed by some 4K displays and other setups. There's also a need for DisplayPort MST with some ThinkPad dock setups.
David has now posted working patches for his DP MST code on the DRI-devel mailing list. Right now his code has just been tested on a Lenovo Ultrabook boasting Intel "Haswell" graphics and it's working when connected to external hubs. There's still code that's a work in progress but overall it seems to be working fine. Right now this initial "preview code" works for Intel Haswell hardware with certain DP MST hubs.
The earliest we'll see this code is now for the Linux 3.16 kernel. Stay tuned to Phoronix for updates.