They added Wii, DirectX10, iOS and Android backends while I was there. None of these were ever considered risky and none had more than one person working on it. Each console/platform has it's own quirks in how to optimise the scene for rendering but the having something rendering on screen is pretty much trivial once you have the machinery in place.
I can't speak for Epic, they are making an engine for every possible game and every possible rendering scene which is a harder problem than what we were doing. But the rendering backend isn't the hard part.