Honestly, I have no Idea but they have been working on this for quite a while
and not long ago they released a trailer which means they are definitely at a point where it's becoming somewhat close to done and they should be doing beta testing a month or two or possibly longer but I can say its getting close to done however they still need to look over the obvious things and add to everything as we all know it's going to be pretty customizable for creators but of course they will add to more things upon updates
anyways this is a mystery for the release but it's also very exciting hopefully its not that far away
February/March - name reservations will be opened up.
April/May - Beta playing will be available for everyone.
July/August - Final game release.
Why?: I don't think name reservations are that complicated to do. I think for them it's quite easy to set it up, the only problem is that it's probably not a priority right now. They also said they will take a few extra months to finalize the game before doing a beta. Doing the beta in April/May will give them 3-4 months of extra work to get ready for the beta. I think they will release in July/August because that's the best time since summer vacations. Also I don't think it's realistic to announce a game early 2019 and then wait till end 2019 to release it but we never know.