I think the game is still very, very early on in development. If memory serves me right without going back through the KS updates, they only started actually developing the game about 6-months ago, with everything prior being planning. So for a trailer based off 6-months of development, I'm not too worried, yet.
But I am of the mind that they will not be sacrificing quality, especially seeing how Yu Suzuki is notorious for drawing out development years past initial release windows in order to deliver the best games possible. Sure, he probably does not have this luxury anymore since this game is not being funded by Sega or some other big publisher, but I'm expecting that late 2018 will be the earliest this game will see the light of day, but 2019 or even 2020 may be a possibility. The worst thing they could do is rush this game out the door in a semi-finished state; it would spell the end of the franchise for good. According to Suzuki one more game (aka Shenmue 4) would be needed to tie up the story, so this needs to succeed if we are ever to get a conclusion to this franchise.