This seems pretty standard to me, and I didn't really expect any new material until late 2018 at the EARLIEST. The band has stated that they have the future of the band mapped out until about 2020 or so, which sounds like they know approximately when the next album and touring cycle are due.
I think it's impossible to expect any less than a three year gap between albums anymore. The albums are much bigger in scale than they once were, and they tour much more widely than they used to. They deserve to have a break after two years of intense touring, and I'm fine with allowing them as much time as necessary to do what they need to do (side projects, some family creation/bonding time, gathering new inspiration) in order to deliver us something incredible for NW9. We assume that the year long break will involve no writing on Tuomas' part, but that might not be the case either. The early 2018 date might just indicate the point where Nightwish will gather to begin arranging what Tuomas has composed during 2017. This could mean a new album by the end of 2018/early 2019, and then touring across 2019-2020. This is still only a 3-4 year gap between albums, and fits the timeline most of us have anticipated.
We have so much to keep us occupied in the meantime, and I'm pretty sure a post-tour DVD will tide any of our latent Nightwish cravings over during the break. It seems like it's going to be a long time, but it really isn't. Time goes quickly... I mean, come on - Imaginaerum was released almost FIVE years ago .