This must be possible. The system partition is mounted ext4 (being a Linux based system, the kernel naturally has native support for it!)
Is the microsd slot always the /dev/block/vold device (in which case mounting will be easy), or is the Linux device mapper framework being used to control this? The mounting mechanism seems way more complicated than on my Asus Transformer. I just mount /dev/sdc1 on that.
This really annoys me. Android is built on Linux, but doesn't support mounting of Linux formatted sd cards out of the box. Up until recently this hasn't been a problem as you can just use FAT32, but now we are doing things like storing big HD videos on our phones, the 4GB file limit is becoming a serious issue. This is exacerbated for me by the other pain of MTP only file transfers which simply don't work under Linux.
Hint Google, don't grab a huge chunk of OS code for commercial purposes and then ignore the users of the very system you're basing your product on! Everything required is present and this all should just work for us Linux users.
