To my knowledge there is only 3 types:
1 Shoot until fill, then switch
2 Shoot the same thing to both cards so you have a copy
3 Shoot one file type to one and one to the other
Why is there no option to shoot the first image to card 1, second to card 2, third to card 1 etc.? Let's assume you lose a card in all 3 of the current types of writing options assuming you have two full cards.
1. You lose half of your pictures in a big chunk (i.e. first half of day or second half of day)
2. You are fine but you are limited to half as much space (as it is mirror if you have two 32 gig cards you can only shoot 32 gigs of photos)
3. You potentially lose all of your raw files. JPGs lost probably won't matter.
If you alternate cards and lose a card you can still potentially have every photo. For example in a wedding, if you lost a card, you would still have a story from the whole day on the second card. Sure you might not have a specific shot of the bride getting ready, but you will have some because the 4 shots you took of the bride tying her dress got divided up to two cards. Whereas if you were filling both cards and you lost one you would lose the first part of your day.
It also serves to maximize your memory. If you shoot two 32 gig cards you essentially have 64 gigs of photos. If you lose one of them, instead of taking a chunk out of your story, it kind of "thins" the photos from throughout the whole shoot.