I'm suggesting this because once hive 2 goes up, aliens jump up in power. Why?
Abilities
*Skulk leap - skulks can close distance suddenly! And they're hard to hit! They become much more effective.
*Fade metabolize - he doesn't have to worry about energy, doesn't have to go back to the hive for a heal
*Gorge bilebomb - the best way to take out eleced structures
Armor
Alien armor gets more powerful at second hive. Kind of like armor upgrades
Chambers
Another set of upgrades!
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My idea: the alien equivalent of an arms lab. Don't know what to call it yet.
It would be a structure that upgrades alien armor, maybe damage if the devs so choose. The hive would no longer affect alien armor; that responsibility would go to this chamber. Don't know how many you would build... 3 for each hive? Or 1 for each hive? But they'd be restricted by hive - couldn't build them any earlier or later than you can now.
Everything else would stay the same. Build time and res cost would be tweaked to make it the same cost as a hive. It wouldn't change the timing or quality of the upgrades aliens get. It would just split one thing off from the hive.
The reason for this tweak would be to reduce the slippery slope effect of a hive rush. Because hives are so important, second hive rushes are often make-or-break for the marines. This would reduce hive importantance by splitting it up.
Instead of the binary you killed the hive or you didn't, we get a new level in between.