They have mentioned it in a few different videos they been wanting to wrap up 7DTD to do another zombie game but without the building/destruction aspect because it will give them more freedom to do different things. I think evidence points to that's what they have already started, they have more than tripled their staff (According to their videos), but are developing as a significantly slower pace than they ever have before. They have the largest team they have ever had, but this is the longest wait for an update they have also ever had despite it not being that significantly different. Take a look at Alpha 16, comparably not much smaller update than the new A17 but despite significantly larger staff its taken almost twice as long as A16 already. I'm sure before the end of this year we will hear about their next game they have been spending so much time/money on.
They (Madmole) constantly comments about the difficulties they have had getting their Minecraft-style building to perform well and I think they want to get away from it because they can't seem to get it running very well even after almost 7-8 years of development (i.e. micro studders, constant bugs, overall FPS issues, etc etc etc).
Please don't get me wrong, I LOVE this game and don't criticize it without pause, I have put in like 1500 hours into this, but facts are facts.