Someone has been rootling about in the files of Mario Kart Tour, and as a result has come across information pertaining to some Battle Mode content.
The content in question was found by Koopavocelot (via kart_tour), and reveals new battle courses with sound files for GCN Cookie Land, DS Twilight House, Tour Paris Promenade, New York Minute and GBA Battle Course 1.
This, of course, may not mean a Battle Mode is coming to Mario Kart Tour, but its an interesting thought.