There have been rumors flying around for a new Nintendo Switch model in the next few years and now Nintendo themselves have started the possible prep-work.
Live on their official YouTube channel right now is a "how to prepare a Nintendo Switch for Trade-In or Sale" video, labeled as a "Consumer Service." It basically tells you to back up your save data with the cloud save feature (restricted to Switch Online users), do a system transfer and link your accounts, then erase your data. You can also unlink your account online if you forget to delete anything before trading it in.
It's helpful regardless of whether or not a new Switch is even on the horizon, and falls in line with their "multiple Switch units per household" vision. It's just a shame the backup tool isn't nearly as cute as the Pikmin-themed one on Wii U!