Well, talk about a surprise. We heard about the Mario X Rabbids RPG in the past but this is brand new information on the title.
Yes, the Grant Kirkhope, composer famous for his work at Rareware, is making music for a Super Mario title! Granted it is not a mainline Mario game but this is huge news if the rumors is true. Laura Kate Dale has been correct about various Nintendo rumors in the past, so I think it is safe to say she might be right about this information. It is worth noting that she has two sources backing up this claim as well.
But word of warning: This is a rumor and please do not take it as fact until officially announced by Nintendo, Grant Kirkhope and/or Ubisoft. This wouldn’t be the first time Grant did composition work for a role playing game; he did the soundtrack for Kingdoms of Amalur: Reckoning a few years back.