For those who do not know: Gold enemies are invicible. Godmode. Unkillable. They have endless health.
This would add more of a challenge to the level, since the mentioned turrets deal their corresponding damage and spread multiple bullets across the area. If OOO thinks Gold-style enemies do not match the UP & it's swarmy theme, they could just put some swarm designs over them and call it a day.

Additionally, I suggest a Gold Trojan to spawn in the elite variation of the UP's last arena.