I'm a long time OpenWRT user and tinkerer but this is my first attempt at actually bringing OpenWRT to a yet unsupported platform.
I've created a github repository with my initial effort and findings at https://github.com/ggiraudon/c5400x-openwrt
What is interesting is that the official firmware from TP-Link is actually OpenWRT 12.09rc1 (reskinned by TP-Link).
Also interesting is that non of the OpenWRT stuff is included in the GPL package they have on their website for this model, nor is it mentioned anywhere on the TPLink website.
I only figured it out after extracting the firmware's file system.
If anyone has had any experience in a similar process (porting OpenWRT to an unsupported CPU), I would welcome any pointers. In the mean time I will continue investigating and report what I find.