A few studios I can think of could have something lined up based on previous release cycles.
Camelot-for almost a decade they release a Mario Golf/Tennis game roughly every 2 years (Tennis Open-May 2012, World Tour-May 2014, Ultra Smash-Nov 2015, Aces-June 2018) so a new Golf title is possible.
HAL Labs-they release a traditional Kirby title roughly every 2 years (Return to Dreamland-Oct 2011, Triple Deluxe-Jan 2014, Planet Robobot-April 2016, Star Allies-March 2018) on top of being able to release spinoffs and smaller titles in between.
NDcube-like the other studios listed, they release at least 1 game every 2 years (2013-Party U/Island Tour, 2015-MP10/Amiibo Festival, 2016-Star Rush, 2017-Top 100, 2018-Super MP) so either a new Mario Party or a Wii Party spiritual successor.
Inti Systems-Even though Fire Emblem released just a few months ago, IIRC only about 40 of their 150 team members worked on it so a new Paper Mario is very possible.
When the herd loses its way, the shepard must kill the bull that leads them astray.