Archetype is what happens when a True Ancestor (a
"seed of CM's potential" produced by
a reality marble) has a body of sufficient
purity and
power (eg.
one able to recreate the Millennium Castle and so be marked as "Brunestud"; consider also that along with [or because of] losing some of her power
Arcueid cannot assume the form of the Princess until she retrieves her hair) which causes
the aspect latent in each and every True Ancestor as beings that are
"the same but different" to CM to manifest. In Arcueid's case,
what keeps her from "becoming CM" is her sense of self and an inability to
"accept CM in her current state", which may yet
wear away in her imprisonment and leave the way open for the aspect of CM to take over. Hence Archetype is both
"the princess of the True Ancestors, Arcueid's true form (not in her intended role as the executioner of the TA but as a being that can "become CM") and currently a
possibility, the
"shadow of Arcueid Brunestud". Were the aspect of CM to take over, his plan to
be reborn as part of the order that would inevitably
reject him in his original form would be complete.
At this point one thing should be considered: talking about a "rebirth" of CM-as-an-individual in terms of his essence/soul/what-have-you as transmigrating into/possessing a body is not supported by the mechanics he put in place. He desires to
maintain his "will" and
embeds a "principle known as CM" within the TA. When this principle/will takes control of a body which matches the specifications of CM's power and purity, out comes a being that thinks and acts like CM while boasting abilities equal to CM - a
successor in every way. As Shiki discerns,
if it's an aspect of the original, it's the same as the original no matter how it looks. The rebirth of CM is most likely a figurative one through the creation of a being that is practically the same as the original. Whether his goal is to bend the planet to his will as its brain or enact the plan alluded to in the fable of the Prologue, it should not matter in the slightest whether it is his original self or his identical daughterclone doing it. Of course,
whether or not it can really be pulled off is another matter.