Many fans thought that the reason why Project M stopped developing has something to do with Nintendo sending them a cease and desist letter. The dev team's attorney and business consultant Ryan Morrison clarified:
To clarify: We weren't contacted, issued a C&D, threatened or had legal action taken against us in any way, but we want it to stay that way.
— Video Game Attorney (@MrRyanMorrison) December 2, 2015
[Source: Kotaku, Gematsu]