"Yeah, but wouldn't you consider that was also done by having mystery in those games?"
Not really. I consider it more about telling the story primarily through visuals.
Take the Mother Brain battle. There is not really a whole lot of mystery -- in fact, I would argue it is the opposite, and that the scene works because players intuitively grasp exactly what is going on and exactly why in spite of the fact that there is not even a single word spoken.
"I mean from a meta point of view we're so acquainted to the franchise at this point that rolling back to Metroids, Space pirates and the common enemies might not be enough for this franchise to grow."
You are talking to someone who thinks that they ever release another Metroid game set on Zebes, SR388, or space station recreations of Zebes or SR388, it will be too soon.
Personally, I am fine with Samus fighting a race of inter-dimensional shadow-ticks. I am fine (conceptually) with Samus investigating an ancient civilization and coming into conflict with other bounty hunters. I am fine with... uh... uh...
wow, those are really the only times Nintendo ever really explored anything but pirates and alien jellyfish, huh.
Oh, I was also fine with everything in the Prime 1.5 proposal. That sounded cool.
There are a gazillion stories Nintendo *could* be telling with Samus but choose not to.
"It's also a tricky thing since it kind of feels like people might be happy if Nintendo just makes a remake to Super Metroid."
That would be preferable to their current treatment of the Metroid franchise but still suboptimal imo.
"then again that's what they have done and it's a direction that hasn't been well received."
For the record, the worst-selling Metroid titles (and the only ones to not break a million in sales) are Zero Mission (remake of NEStroid), Pinball (Remake of Prime), New Play Control Prime Trilogy (re-release of the three Prime games), Other M (which recycles basically all of its story elements from Fusion), and Federation Force.
If there is a direction of Metroid games that has not been commercially-successful, then it is the direction of re-issuing games we have already played.
(And I guess chibi-styled co-op shooters on handheld consoles.)