One (little) feature request: As the system already uses ext4 for internal partition, please allow the usage of ext4 partitions in the "shared medium" variant of the sd-card as well. exfat would be even better ;-) Currently, only fat32 is permitted, which can't handle files bigger than 4 GB, which is a problem for e.g. offline wikipedias. Android wants to format sdcard with any other file system.
I know that there are unofficial ways for rooted Android, but this would be a nice (and probably easy) feature for the "normal" Android.