I think the good news that we can take from this is that Nintendo is finally committed to making a decent Metroid Prime game and that they learned their lesson from the Federation Force disaster. I think almost every Metroid fan out their would rather just not have another Metroid than have anything less than the best effort from Nintendo. To me, this broadcast indicates that Nintendo now understands this about their fans. Regardless of whether Retro Studios is currently up to the task, Nintendo is clearly showing that they are willing to staff the studio up or provide Retro with the necessary support to make the game a success. Nintendo's commitment to making something decent is far more important in my opinion than which studio develops the game.
Hopefully, this will mean that Metroid Prime 4 will be Metroid's equivalent to BotW and will really move the franchise ahead. My biggest fear was that we would get a Metroid Prime 3 with updated graphics which was OK in 2007 but would be an absolute disaster in 2019. The entire gameplay mechanic and world design needs to be re-conceived, hopefully around the open world concept. MP4 cannot be formulaic re-release, it has to be what Metroid Prime was to Super Metroid.
The bad news is that the game is probably a long ways away. It took Nintendo about 5 years of intense development to get BotW ready and I would suspect that it will be something similar for Metroid (maybe it can be done in 3-4 tops). But remember, the only way that this game would be coming out quickly would be if it was crappy formulaic re-release. I would rather have it be a launch title on Nintendo's next console then get another Federation Force or Star Fox Zero any day.