EMMC is where your media is stored, music videos etc, you only need to reflash the firmware, the EMMC has nothing to do with rootfs or applications, after flashing my firmware to pr1.1.1 global version i had about 60mb rootfs spave left, apparently with pr1.2 it will be more like 90mb.

EDIT, Be careful with the stuff in the wiki the moving the microb and maps one is ok as is optifying python, but the scripts in there can cause alot of problems/slowdowns, id stear clear unless you understand exactly what they do, i have, and i would only use them if i had to, like to gain space for ota firmware upgrade which when complete would reverse the detrimental changes anyway (someone please correct me if this is wrong)