I recently spoke with Kynan Pearson, who worked as a designer on Metroid Prime 2 and 3. He's very keen on the idea of having an open-world game in the series, and his argument is quite solid.
www.destructoid.com/metroid-prim...
destructoid.com
Metroid Prime 3's Kynan Pearson discusses abandoned ideas and makes the case for open-world
An open-ended Metroid Prime game would definitely be welcome.