@Kerrida - I completely agree that they should focus on the game and then the tools, but there is also a downside to releasing the tools later. Waiting to long might make it an uphill battle to spread the word. That happened to the Witcher 2's tool, which was released two years after the game's first release on PC. They seem to have more luck with Witcher 3's editor, and I don't even think it contains a level editor.
If Larian release the tools with the game or soon enough that they can still ride the buzz of the release. I think there is a far bigger chance they would become popular. I think it's a strong message to send to the consumers that the GM-mode is there from the start, because it is part of the game and not an after thought.