This can happen when Maemo can't mount /home. I've been thinking what could've gone wrong, and it seems that I've made a very unfortunate error in my post.

Nokia has made Maemo in such a way that it recreates fstab every time it gets booted. The first partition that identifies itself as FAT is used as MyDocs and the first one to identify itself as a Linux native partition is used as /home.

By executing sfdisk -c /dev/mmcblk0 1 83 MyDocs won't get mounted as it identifies itself as not being FAT anymore, but rather as a Linux native partition.
Now Maemo tries to mount it as /home as mmcblk0p1 gets checked earlier than mmcblk0p2. Of course, the content of /home isn't on mmcblk0p1, causing Maemo to get into a reboot loop.

I didn't notice the error as I've partitioned my eMMC differently and changed rcS-late to recreate fstab in a static way.

I'm afraid a reflash is required. Flashing only the rootfs should be enough to get your device working again (you won't lose any contact/personal data). Applications will need to be reinstalled probably though.

I've edited my post above to set mmcblk0p1 to a different partition type than 83 to make sure this won't happen to someone else.