So far this does not look like any more customization than you can do for any other smartphone. I can get any number of colored or shaped cases for my SGS3. Apple has offered custom ingraving too. I am not seeing anything compelling other than the new sensors.
Want to offer customization Motor...err, Google, then put in an SG slot, you know what those are, the memory slots that have been on phones, even the free dumb phones, for years, so I can choose how much storage I want.
Also make it with a removable battery so I can swap it out so I can continue to use it without having to search for an outlet, and carry my charger around, in the afternoon.
Basically.... like the Nokia 820... which the whole CASE is replaceable, which I think is a great idea. You have a BASIC phone which you can put any kind of body on you want... Motorolas or someone else... without adding bulk.
@tntom : there is a difference in buying a case to go over a case on a phone. With the Galaxy phones, when you scratch up or damage the original case... well, too bad. Here, you can replace the case...
The Case-shells ADD bulk to phones. Hence, I never buy a case-cover, the phone is already big enough. With this, you can mark it up all you want, just replace the body.