UPDATE – Screenshots added from another site.
Sorry I don’t really have time to investigate right now but take a look at this link in the mean time. I can’t see it being true myself but I’ve been wrong before. To my eye this looks too similar to Fenix 3 so there’s no reason to skip 4 and move to 5. The USB c connector might happen, but I’d rather see a magnetic connector which doesn’t have an irritating post in the middle of it. Garmin have learned this lesson before with connector comfort so unlikely to repeat so soon. https://appelmoessite.wordpress.com/2016/11/08/the-new-fenix-5-and-5s/
Garmin seem to be trying to remove the leak, and some bloggers who deal with them have been asked to take down the story. This site doesn’t deal with Garmin and I never post their copyright pictures, only screenshots of interesting things I see on the web so we should be safe here 🙂