The website doesn't work for me at the moment, but I watched some videos of RE on YouTube.
There will be some kind of an in-engine editor, mainly to be able to see the appearance of objects while material mapping, as you'll never get an equal lighting outside the engine. Later there will be also procedural materials supported that will be mappable solely through the editor.
However, it won't be nowhere near as complex as the editor in Neoaxis. Apart from it being a lot of work, we don't need to differentiate from other engines this way, to catch every developer we can. And we are not fans of complex GUIs that also define the gameplay and everything, it'll be mostly textual here - config files and scripts. The hard way