So, there seems to be examples of previous models of Nexus replicants in existing media, notably the current Blade Runner: Origin series of graphic novels.
There doesn't appear to be much variance so I'll not be making use of those, they don't quite hit the mark for what I want in my games.
This is a rough draft of how I'll probably take the Nexus line in my alternate Blade Runner setting.
Nexus
A breakthrough in immunology and cell development allowed the creation of a processor from neurones.
Still little more than a PhD project when a coronal mass ejection caused significant damage to powergrids and silicon based processors.
Nexus 1
A hasty roll out to take advantage from the reeling silicon CPU suppliers. This was still effectively a prototype, housed in a large enclosure powered by biocells, and fed by biomass cartridges. Easily swapped cables allowed it to interface with a myriad of equipment.
Nexus 2
A refinement and miniaturisation of the previous generation. The core is small enough to be placed in a free roaming robotic chassis. While the core is standard the chassis styles are diverse.
Nexus 3
The first humanoid model, and also the first to integrate other organic systems, most notably sensory input, into the mix.
Nexus 4
The first model to be indistinguishable from a human at a glance. Several systems, most notably digestive and waste processing, are not yet organic.
Extremely prevalent in care and assistance roles.
Nexus 5
Fully organic, and the first model to incorporate hormonal regulation.
It has been observed that this model exhibits an abundance of quirks and can rapidly diverge from expected norms of behaviour.