I don't think it comes as a surprise to anyone. The announcement itself was terrible and treated very poorly. I can guarantee that in 2017 (that far back eh?) that there was nothing but that trailer. If anything, there were just high level discussions among developers and possibly very basic concepts developed.
Going into 2018, I would imagine that were was some significant development allocated towards the game but I'm glad they went public with the announcement. Retro Studios crafted the modern Metroid back in 2002 and I very happy to hear Nintendo acknowledges that it is far too risky to challenge the expectations of a sequel to Metroid Prime with any other developer.
In all honesty, I wanted the Prime series to end. However, I was eagerly looking forward to a new Metroid game. Given that it is a continuation of the Prime Universe, let's see what Retro Studios can do. After all, they have an excellent track record.
Since the previous developer was Bandai Namco Singapore, I think it was a fair judgment call. The brand and name of Metroid is too high profile to take the risk. Look at Other M as a "prime" example. Good game but did not live up to expectations.
For what it's worth, Metroid Prime remains my all-time favourite video game.
So if anyone is excited to see where this franchise goes... it's me