There is a possibility a strategy map editor may be released, but what they are using now would need a lot of work to make it user friendly. An RTS map editor will not be released, due to the complexity of the process they are using. I don't think there has been anything official about an editor to mod anything else.
Nothing has been announced for the near future. Larian should be switching over to mostly focus on Divinity: Original Sin until that game is finish (the kickstarter estimated November, but with DC being delayed a month, that might cause a delay with D:OS, as well). After that, I guess time will tell.