To start with, my borg character has an MMI. But I've noticed sometimes they have a positronic brain, I think from when they join mid round, maybe?
This is kind of annoying from an RP/Character perspective, as those are pretty different backgrounds from each other. It's really awkward mentioning your past human life as a borg, only to get removed from your chassis and see a positronic brain. So it'd be great if there could be a trait or something to keep consistent what kind of brain you have in these, one that forces you to have the right brain type.
I'm excluding stuff like derelict cyborgs of course.