Dear Funimation!
Since we know that Is This a Zombie will be a DVD only release and we can assume the same for Deadman Wonderland, I have a suggestion for the LE extra:
Could you please provide an art-booklet for the Limited Edition of these shows?
A booklet like the one for the Rosario & Vampire LE and the one RS gives for Cat Planet Cuties. Both shows have enough material to make a nice booklet, so please:)
The postcards that came with Heaven's Lost Property S2 are nice too, but a booklet would be better in my opinion 
They seem to only do art books when they are unable to provide a Blu-ray.
Not true! Both Cat Planet Cuties and (the upcoming) Freezing got an art booklet and both of them are BD/DVD combo packs.
They are exclusive to Right Stuf customers though.
Avatar: Rosette and Chrono from Chrono Crusade
I think you'd have to talk to RightStuf about that. I don't think FUNimation does external extras like that. The only external extras they usually do are postcards (like the ones that came with Heaven's Lost Property Forte and Hero Tales) and artboxes (like Panty & Stocking, Heaven's Lost Property, Rosario + Vampire, and Cat Planet Cuties). Other than that, you have to talk to the retailer.
If You're Reading This, You Have Too Much Time On Your Hands...
The LE extra for Is this a Zombie? is a gift.
Locomotion
animation, young adults, digital era
No, retailers can't just create extras like that willynilly. The artbooks are created by FUNi using artwork provided by the Japanese license holder, and offered through retailers like Right Stuf as an incentive to get customers to buy something they may have been on the fence about.