>> btrfs would also be an issue. But, does it make sense to have btrfs on
>> a flash disk? I don't check for reiserfs, xfs, ... in initrd either.
>Why not? I use BTRFS on a SSD here and it works well.
>While I don´t think that BTRFS adapts to ordinary USB sticks like it does
>for SSDs, I think it will work just fine.
Sometimes, however, it is useful to lose a the edits of a session: to keep this ability, the USB key is formatted as btrfs, using its snapshotting feature to keep a backup of previous sessions. This unluckily means that a bigger USB key is needed: with smaller keys ( < 4GB) you can probably expect to have about 1/4 of the space available for the system.
btrfs was one system with rather large result spread in that test, which does not make it an obvious candidate for me. The question for me is, does it really make a difference in some respects? It seems to do, but partly both ways. Which is why I would tend to stay with ext3/4 when going beyond FAT32 in this case.