I am currently working with the TP-Link TL-WDR4300 (also TL-WDR3600/TL-WDR4310). I believe its firmware images are in the same format as the device you mention, so I will be making sure the FMK works with these images soon. They are a very simple format, not obfuscated.
I've actually found the TP-Link vendor firmware quite awesome. It's particularly advantageous because it supports the routers Hardware NAT, a feature missing from all aftermarket firmwares. It is also completely open source and is ready to run custom packages.
I strongly recommend sticking with the vendor firmware, and using it as a base to modify rather than DD-WRT. Hardware NAT alone is reason enough to do this, and compared to DD-WRT, the TP-Link source code is easier to work with. Of course, with the FMK you need not work with any source code.
I will confirm when I've added support for TP-Link routers. If you want to expedite the process, you can always pay me

. Otherwise, it shouldn't be long at all.