I think it will be more complex to implement that kind of network type prioritisation. Suppose that you want to prioritise IPv6 over IPv4. How do you manage the threshold of the number of IPv6 peers before you allow IPv4 peers to be connected to the node and being connected from the node? How about if the nodes would never reach that threshold, resulting you have less IPv6 peers and no IPv4 peer for a long time? Would you use a dynamic timer to avoid that issue? As the network is dynamic, would you keep maintaining the number of IPv6 peers to always above the threshold regularly? Or would you manage that base on the timer? And so on

And if you manage to find the solution for that without increasing MAX_OUTBOUND_CONNECTIONS or the maximum outbound connection slots remain 8, the chances that the node will have less IPv4 peers for longer time than before the implementation of your solution is quite high.