Interesting list there, i'm also a believer for Odyssey 2 but listening to the MinnMax podcast, they made a good point on how the direct sequel to a 3D Mario game happened in only one instance with Galaxy and Galaxy 2.
So i think the next 3D Mario game will be an evolution of Odyssey but not a direct sequel.
Also if one of the rumored Wii U ports for 2020 is Super Mario 3D World, then i don't see Nintendo releasing 2 3D Mario games in the same year on the same platform.
Anyway there's another series that people often forget because of Prime 4, and that's
2D Metroid.
This is my case for a new 2D Metroid possibly released in 2020, and i'll do it presenting a list of facts:
No. 1 - Back in 2015 MercurySteam pitched to Nintendo a new entry in the Metroid series for both Wii U and 3DS.
This was reported by
LiamRobertson on Nintendo Life , as one of the devs tried to leak the game, other evidences were found later. The pitch was rumored to be rejected by Nintendo.
In 2016 MercurySteam co-founder dismissed the rumors calling them bullshit, but then at E3 2017 Nintendo revealed Metroid Samus Returns for the 3DS which was indeed developed by the spanish studio with the guidance of the legendary Yoshio Sakamoto.
Metroid Samus Returns was overall a success and Sakamoto was very happy about how development went with MercurySteam.
That means MercurySteam still has a working prototype of an HD Metroid game for Wii U which could be reworked and ported to Switch.
No. 2 - MercurySteam hasn't announced or released a video game since 2017.
They released both Metroid Samus Returns and Spacelords in September of 2017, since then only updates for their online games and not much else. The time is right for a new entry.
en.wikipedia.org
No. 3 - Metroid Samus Returns teased a possible premise for a new 2D Metroid game.
No. 4 - Metroid Prime 4 development has been scrapped and restarted last year.
Meaning we won't see it for a while, Nintendo may need some form of Metroid release to fill the gap in the meantime whether is a new 2D entry or Metroid Prime Trilogy we don't know.
Now my only argument against it is that on September of last year, Sakamoto announced that he has been working with Mages on the remake of Famicom Detective Club, a japanese only release.
That said it's possible he has been working on both, after all he was Producer of Samus Returns not Director.