I've found William Rittenhouse in my family. I was excited to see the Holy Roman connection but was skeptical. I had gone on a wild goose chase before trying to connect Elizabeth I to my family and ended up not being able to collaborate that so I felt that this time I needed to look into it more before adding all these German Kings in there. From what I can tell, the rumors of being related to the Hapsburg royal family was a long standing belief among the Rittenhouse family. Historian David Kolb Cassel collaborated with many Rittenhause family members and wrote A Genea-Biographical History of the Rittenhouse Family in 1893. The prologue to this work claimed that Balshaser and Max II were the same.
But more recently, Dutch paper historian Henk Voorn unearthed some documents putting to rest the origins of the Rittenhouse family. The Rittenhouse Mill and the Beginnings of Papermaking in America by James Green highlights this in page 4.