Since Tomato firmware is developed for free, I believe developers of any of the branches has to be *extremely* motivated personally to port the code to compile for Atheros. It appears most of development effort is currently around increasing NVRAM size and IPV6.
Given this fact, I believe one or two person's monetary contribution to any of them would be too low to motivate any serious development to port to Atheros. In addition, they would probably require also a physical Atheros router donation to facilitate any given testing.
There is dd-wrt option for that router. If there is a pressing need to absolutely run Tomato in your environment, I believe the most productive option (for users who desire Tomato and for developers' time) is to sell off that TP-Link and buy a supported Broadcomm router. TP-Link is equally popular in my region because they match other brands for feature and priced themselves lowest against any competition.