I'm not sure I like the black hole thing. If it's done the way I'm guessing it'll be done, it'll be more like levels, or branching paths. I feel like having systems isolated in a void (like planets are isolated in a void within systems) would allow for a better higher strategic game. Plus, with a more open map and the ability to have multiple fleets moving at once you could recreate that legendary Tyranid look, with huge tendrils spreading through the sector and engulfing whole star systems.
A possibly better way is to have the swarm gather minerals from conquered planets, which can then be turned into some organic superweapon to blow up the star for the black hole, or the warp drive thingy. This allows you to leave difficult planets alone for a while, but not to long, as well as allowing you to come back on your steps to defeat them. Having some sort of jump gates/ systems allowing for easy travel between certain systems would add some strategy too.
I like the concept but...once you've sucked one planet dry, it's more of the same.
Needs new challenges as you go.
This can be done in a variety of ways.
Different planets: Either different sort of planets, or by the addition of booster. Can probably be combined.
-An Artic planet would have lots of water, but nearly no trees and the water would take longer to gather. Ships and swarm members spawned by water/trees from an iceplanet would be slower but stronger.
-A molten planet would have equally no trees and no water, but large amounts of minerals, which can be used in the construction of a variety of superweapons.
-A jungle planet has lots of trees and water, but the resulting swarm members are weaker and faster.
-A desert planet has nearly no trees or water, and the resulting swarm members are more dangerous.
-Moons are basically small planets, in orbit around a planet.
-Gas giants are large planets without surface. The swarm can try to gather water from the athmosphere, which is slow.
-An asteroid is a little smaller than a moon, and contains only some ice(hard to gather water) and minerals. Fully colonizing an asteroid before it crashes into the sun or something gives you a rather large but suicidal ship.
-Human reaction. Humans should try to expand their ground, gathering minerals to build ships, sometimes polluting water(weaker swarm members, slower gathering ?) and building new towers and units to annoy you.