The roadmap they claim literally has question marks next to all the dates. This is a rumour mill roadmap, as in tech sites or forums came up with their own made up roadmap based on rumours. You will never in the history of the universe, get an official roadmap from a company that questions everything new on it. Everything else that link suggests is made up.
I will never for the life of me work out why people read this stuff as fact. Not least when it's so obvious they are trolling for hits and the rumours randomly get made up right after any real news. So Samsung officially announce HBM2 goes into production and later that same day all the usual troll tech sites are making up rumours about how close that means some product is.
Nvidia aren't talking, they released no information the day Samsung made their announcement. It's a combination of people on forums with no clue who think 1 + 1 = eleventy billion, and tech sites who use any excuse to get hits. Samsung say something about graphics memory, throw around massive amounts of rumours.
For instance GDDR5x, Micron talk about it, suddenly it's on every single card that isn't HBM in graphics cards moving forward. Not sure that Nvidia or AMD have said much if anything about it but before either said anything everyone was convinced it had totally replaced gddr5 despite not being in production yet. Simple fact, Nvidia are still showing Maxwell when talking about Pascal products, they've shown no cores let alone working demos or full cards. They are way behind and it sounds quite probably they haven't got the first working silicon back yet. April is no chance at all, I think August will be pushing it.