Yeah I think the dojutsus have to be of a certain level to be able to be considered a path, which could be why he gave Nagato the rinnegan to progress the eye's abilities. But I disagree that Uchiha DNA is one of the paths because everyone, except Kakashi, that has had the sharingan has had Uchiha DNA - Kakashi would've still possessed Uchiha DNA in the eye however.I still think Madara's going to grab himself some Hinata byakugan. 3 dojutsus + tailed beasts + the 'body' (senju dna) + the 'spirit' (uchiha dna) makes for 6 paths.
I think the sharingan has to be at EMS and byakugan would have to be at a new level that hasn't been introduced yet