I feel "Monster Hunter" would be the BEST fit due to all of the MH games Nintendo has seen over the years. Dante would be a good pick too, especially if it segways into a Switch version of DMC trilogy announcement soon.
The main character of Dragon Quest XI would be a smart choice to promote the Switch release coming in 2019. HOWEVER Sora would be the most popular choice, and after Joker, nothing would suprise me at this point.
Goku is the obvious choice here, just to troll all the people who do not want him in because of his anime roots. We have had DBFighterZ and Xeniverse 2 come to Switch. He fits more than people would like to admit.
One of the Champions from BotW would be nice. Revali or Daruk would be most preferable to me. Then again, Urbosa is a total badass and would fit right in as well.