The website in TP-Link China have just announced a new device, which the outlook is very similar to MR13U.
http://www.tp-link.com.cn/pages/promos/ … 013-09-26/
I believe this should be an ideal device if it can be ported to openwrt, it comes with 3G simcard support build-in, SD card slot...and 10400mAh batteries! Is there anybody who got more information on this?