Developer editions of the Galaxy S4 have appeared on Samsung's site, and they have their sights set on AT&T and Verizon customers. Note, this is not the $649 Nexus-like version that Google unveiled at Google I/O. This developer edition is good for tinkerers who still want all of Samsung's software and Verizon customers who really don't have any other option if they want a Galaxy S4 with an unlocked bootloader. Variants for both carriers seem to be only offered in Black Mist color.
While it's not unreasonably difficult to root the consumer version of the phone, there is a certain peace of mind that comes with using a device that doesn't require the hassle. Release dates haven't been unveiled yet, nor have prices, but I imagine they won't be low enough to draw any more applause than the Google I/O model received.