From Android Community's write-up:
We are just a week away from the first ever Project Ara Developers Conference and the marketing wheel behind the modular smartphone is heating up. This latest bit of information comes directly from Google, who has just released a preview of the Module Developers Kit or MDK.
Unlike most development kits, which commonly address the software side of gadgets, the MDK primarily targets hardware manufacturers or OEM's who will be creating compatible modules. Google itself has no or little plans to create modules, probably outside very basic ones, and will instead be licensing the modules. It will, however, be creating the officially approved endoskeleton or "endo" that provides the frame and core connections of the module smartphone.
There are two main groups of modules. Front modules, like those for displays, speakers, etc, take up the entire width of the device and are only limited from one up to three modules at a time and nothing more. Rear modules, on the other hand, have more variety and come in three sizes of 1x1, 1x2, and 2x2. The endo dictates the placement of the modules and the MDK states the sizes for officially sanctioned ones, though it gives certain exceptions to very specific modules. At the moment, Google isn't supporting third-party modules, though it's not hard to imagine some of them popping up in the market when and if Project Ara truly takes off.
Read the full article here.
Fascinating stuff, and from an engineering standpoint it looks quite 'doable', even if the end result won't be anywhere near as sleek and refined as specific manufacturer 'holistic' designs. I'd put the timescale for working prototypes well into 2015 and possibly 2016 for anything which could be bought by end users. Assuming that there's a profitable market for such 'identikit' phones in the first place?
Success will also rely heavily on the number, quality and price of available modules, which, of course, relies on the cooperation of OEMs and even third-party manufacturers. Google launches the Project Ara Developers Conference next week and we'll get more of an idea about interest and ideas at that time.