system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Is it possible for Borg nanites to assimilate a Founder?
gpt
No. Changelings store some of their mass in a subspace "pocket" they carry around with them, which allows them to take the shape of small items like combadges and rodents. Thus any Changeling, once infected by nanites, could simply morph into something the size of the nanite, thus sending almost all of their mass into the pocket and leaving nothing for the nanites to assimilate.

It is possible that a Changeling infected with Section 31's genovirus could be assimilated, but the Borg would likely have to completely re-engineer their assimilation process and the nanites themselves. After all, it has never been shown that a Borg has assimilated a non-cellular organism, and there was quite some trouble with Species 8472 in this regard.