Both titles are due later this year in Japan.
A recent news article from the Nikkei Shimbun confirmed the existence of Wii Fit Plus and revealed that a new Mario title is in the works.
Wii Fit Plus, which will be released in the fall, will have more precise weighing options and the ability to compare stats and progress with friends online.
According to the article, the new Mario title will be released later this year. Unfortunately, no platform or further information was specified.
Translation thanks to James Charlton