Epic made this announcement earlier today, saying that from "the very first line of code, the very first art created and design decision made, development will happen in the open, as a collaboration between Epic, UT fans and UE4 developers." This will involve frequent forum updates and ongoing discussion as well as regular Twitch streams showing exactly where development stands. Further, all code created during the development of this new Unreal Tournament will be available to Unreal Engine 4 developers via GitHub.
Though obviously this design process will take quite some time, Epic has revealed that the game will appear on PC, Mac and Linux platforms at the very attractive price of "free." Not "free to play," but actually free. Borrowing a page from the Team Fortress 2 playbook, Epic plans to recoup its development costs with an in-game marketplace where modders can sell their creations to players, earning funds which are then split between the modder and Epic itself.
Those interested in joining Unreal Tournament's extended development team should pay a visit to the Unreal Engine forums, where registering a free account is all that's required to offer input on the game's creation.