The only real stumbling block in that group being temperature and fan speed control.
A G5 running it's fans at full speed generates quite a racket.

The NIC might be provided by a card.

If you think about it though, it's hard to believe that just those requirements are holding this back.
After all, isn't it "camp red" that takes a year or more to do network drivers, and how different can temperature and fan speed control be on the 11,2?

We have also heard comments about the developers worries about supporting too many systems.

Anything else would be pure speculation.