[Note: First bug filed]
I'd like to suggest adding more advanced keyfile options (size and offset, specifically) and a 'tempmnt'-like option that allows one to temporarily mount something that is encrypted and use it as a keyfile.
My /boot contains a keys files, which is a LUKS container which consists of keys which are side-by-side on the disk and have to be accessed via --keyfile-offset and --keyfile-size. For extra security I should be able to only temporarily mount /boot/keys.
I suggest that along with target and swap, a tempmnt section can be specified with all the regular options, but it is remembered and detached when everything has been mounted.