There is something intriguing in this.
A collection of Nation “citizens” trying to “settle” a system would be the same as a collection of the (Anti?) Empress’s loyal subjects trying to “settle” a system. It isn’t “settling” and it does not trigger an invitation to participate in elections.
However, we might imagine a terrible conflict affecting Nation. This conflict might disrupt the “hive mind” sufficiently for large numbers of Nation citizens to free themselves from slavery. Some of those former slaves might reach the Federation.
If these people recovered their former identities, their eventual integration into society would be indistinguishable from similar events in recent history, and there would be no “Sansha bloc.”
However, becoming a “citizen” of Nation might disrupt identity so badly that all previous associations are obliterated. The individual becomes “a Sansha.” It is then possible to imagine a sufficient number of “Sansha” settling together such that they gain the power, through direct, representative, or hybrid democracy, to choose their own local leaders, write their own local laws, operate their own local courts, and otherwise run their own local communities as they see fit (subject to constitutional controls). If the size of those communities grows large enough, they would attract the attention of federal political aspirants.
Of course there always remains the question of: “can the mind control be reestablished?”
Ordered liberty does not require the state (small “s”) to ignore obvious risks, and it would be reasonable for the naturalization of persons who escaped Nation slavery to include a period of quarantine - along with substantial ongoing oversight and verification.
However, it is “not impossible” to imagine a “Sansha” bloc in the Federation.