It is widely speculated that Version 3.0.5 may be the final software update for the game on the original Switch hardware, especially as the franchise shifts focus to Mario Kart World on the next-gen console.
Sometimes, the community distributes custom "patched" NSPs that include community-made tracks (like Mario Kart Custom Track distributions) or custom character skins baked directly into the installation package. Safe Installation Practices for CFW mario kart 8 deluxe switch nsp update dlc patched
Here is the story of the "Arms Race" between Nintendo and the homebrew community. It is widely speculated that Version 3