Nintendo will never do it, but one thing they could really do to build on the popularity of the games would just be to embrace fan projects and legitimise the better ones.
Make a deal to see the Galaxy Story mod as official #SuperMarioOdyssey DLC. Put Mario Eclipse on Switch Online instead of vanilla #SuperMarioSunshine. Add the best fan tracks for #MarioKart into the new game. Etc.
They could literally get DLC and new games for maybe a tenth of the usual dev costs and effort.