As I understand it Nichiren taught daimoku in such a way that it would suit people regardless of capacity. Sharp distinctions within the single vehicle doesn't possesses the quality of equality. i.e. buddha and ordinary person are the same. The daimoku is such that those who chant are not separated by these differences but still advance according to cause, capacity and conditions.
I think this is why he shrouds development for higher capacity so it doesn't seem different to those of lower capacity avoiding perceived division among practitioners.
six stages of practice ［六即］ ( roku-soku): Also, six identities. Six stages in the practice of the Lotus Sutra formulated by T’ien-t’ai (538–597) in Great Concentration and Insight. They are as follows: (1) The stage of being a Buddha in theory. At this stage one has not yet heard the correct teaching and is ignorant of Buddhism. Nevertheless, a single moment of life is in itself identical to the truth of the matrix of the Thus Come One; in other words, one is a potential Buddha. (2) The stage of hearing the name and words of the truth. At this stage through the spoken or written word one comes to an intellectual understanding that one has the Buddha nature and that all phenomena are manifestations of the Buddhist Law. This may take place through reading or hearing the words of the sutras. (3) The stage of perception and action. Here one perceives the truth [of the Buddha nature] within oneself through practice, the truth and the wisdom to perceive it are in accord with each other, and one’s words match one’s actions. (4) The stage of resemblance to enlightenment. At this stage, one eliminates the first two of the three categories of illusion and attains purification of the six sense organs. Having advanced this far, one’s wisdom resembles that of a Buddha. In terms of the fifty-two stages of practice, this stage corresponds to the first ten stages, the ten stages of faith. (5) The stage of progressive awakening. This is the stage at which one eradicates all illusions except fundamental darkness and awakens progressively to the truth of one’s Buddha nature. In terms of the fifty-two stages, it corresponds to the eleventh (the first stage of security) through the fifty-first (the stage of near-perfect enlightenment). (6) The stage of ultimate enlightenment, or the highest stage of practice. At this stage, one finally eliminates fundamental darkness and fully manifests the Buddha nature. This corresponds to the stage of perfect enlightenment, the last of the fifty-two stages.
T’ien-t’ai taught that all people at whatever stage of practice are equally endowed with the potential for Buddhahood. In this way he prevented his disciples from falling into the error of self-deprecation or becoming discouraged. On the other hand, possessing the Buddha nature is not the same as attaining Buddhahood. T’ien-t’ai therefore divided practice into six progressive stages to prevent his disciples from falling into the error of arrogance and relaxing their efforts. In Great Concentration and Insight, he states: “If one lacks faith, one will object that it pertains to the lofty realm of the sages, something far beyond the capacity of one’s own wisdom to understand. If one lacks wisdom, one will become puffed up with arrogance and will claim to be the equal of the Buddha.” The Record of the Orally Transmitted Teachings gives Nichiren’s (1222–1282) interpretation of the six stages of practice: “Speaking in terms of the six stages of practice, the Thus Come One in this [‘Life Span’] chapter is an ordinary mortal who is in the first stage, that of being a Buddha in theory. When one reverently accepts Nam-myoho-renge-kyo, one is in the next stage, that of hearing the name and words of the truth. That is, one has for the first time heard the daimoku. When, having heard the daimoku, one proceeds to put it into practice, this is the third stage, that of perception and action. In this stage, one perceives the object of devotion that embodies the three thousand realms in a single moment of life. When one succeeds in overcoming various illusions and obstacles, this is the fourth stage, that of resemblance to enlightenment. When one sets out to convert others, this is the fifth stage, that of progressive awakening. And when one comes at last to the realization that one is a Buddha eternally endowed with the three bodies, then one is a Buddha of the sixth and highest stage, that of ultimate enlightenment.
“Speaking of the chapter as a whole, the idea of gradually overcoming delusions is not the ultimate meaning of the ‘Life Span’ chapter. You should understand that the ultimate meaning of this chapter is that ordinary mortals, just as they are in their original state of being, are Buddhas.
“And if you ask what is the action or practice carried out by the Buddha eternally endowed with the three bodies, it is Nam-myoho-renge-kyo.”