I have to disagree with the others. I personally love concept art (being an artist / designer myself, that’s probably the reason), and if I see some great concept pictures of a project makes me definitely interested in it, even without seeing any real gameplay.
If nothing else, it inspires me and gives me ideas for my own projects, or just makes me feel good by looking at something cool.
Obviously, I will not spend every day going to that projects website, share and talk about it a lot, but if the concept art is amazing, then I will definitely subscribe to the newsletter. I mean, it costs me only a few seconds and if it goes nowhere, I won’t lose any sleep over it.
However the website needs to look very professional, to convince me you have the talent (or better said the will to take the effort) to pull it off. And the accompanying text must show you have a solid concept, that is more than just an idea for - let’s say for example “a multiplayer, zombie survival game with cool features”.
Furthermore, I would only go public in a big way (like spreading the news about your new project on social media, sharing the website, etc.) if you are absolutely sure you will continue with it.
What you can always do though is to publish the concept art on some digital art communities, like artstation. It will get you some comments and first feedback for the ideas, and perhaps even some followers.
Also: When can we see the concept art here?