According to the British website Video Games Chronicle, Nintendo has plans to hold an event in celebration of the plumber's three-and-a-half decade run as the star of his own mainline series. This event will be marked by an announcement that Nintendo will re-release remastered versions of "most of" Mario's "back catalog." There's no indication that this would include off-shoot series like Mario Party/Kart, or any of his sports game. But information is fairly sparse at the moment, and Nintendo has refused to comment.
That said, Eurogamer followed up VGC's report by saying that some of these specific remasters will be Super Mario 64 (1996), Super Mario Sunshine (2002), and Super Mario Galaxy ('07). That first one's been a long time coming.
Other titles to be on the lookout for include Paper Mario and a Super Mario 3D World deluxe version that continues Nintendo's theme of slightly upgrading Wii U titles since nobody really bought that console. Eurogamer's report states that the new 3D World will come with an "array of new levels."
These plans will be revealed in greater detail alongside an announcement about the Nintendo/Universal partnership. Those two have collabarated to put together a Super Nintendo World theme park, in addition to an animated film starring Mario.
Originally Nintendo planned to roll this whole announcement out at E3 in June. But those plans had to be altered due to the current pandemic that has made pretty much all of life suck and, like everything else, ended up getting E3's 2020 show canceled.