I was saying on a thread on Sonic Wiki, why can't we just have games other than Olympics for Mario & Sonic series? Why not Mario & Sonic Strikers or Mario & Sonic Tennis?
Nintendo already has an agreement with second party companies for those.
Strikers game being handled by Next Level Games and tennis game by Camelot Software Planning
(yeah, the same Camelot who made Shining Forces series and was mad at SEGA for not bringing Shining Force III ep2,3 to the west and refused to make Shining games for SEGA again).
It wouldn't be fair and would hurt their products if Nintendo & SEGA made another game with same gameplay.