Lots of theoretical biology threads recently.
No. The speed that necromorphs infect people and convert their biomass into necro stuff would boil them alive. The brethren moons are also entirely silly, and most necromorphs have absurd biologies that would probably be unhelpful.
The closest you would get might be some kind of far, far future bio-nanotech/microtech, where organisms are infected with biological grey goo subverters which then slowly restructure their biology, genetics and psychology into forms that serve their purpose. It's not out of the cards that they could break organisms down into constituent biomass and then fuse it together with that of multiple creatures, making some huge fused monsters with unnaturally efficient biologies. You may see muscles several times stronger and more efficient than anything naturally produced by evolution as well as brains even smarter than ours that do nothing but think of better ways to spread the bionano.

>>16943168
You can take it further than this, thinking about it. Maybe the goo uses the organisms it subverts as processing nodes, which share memories and information via chemical signals and literally connecting and disconnecting nerves to each other, turning the goo into a distributed superintelligence. Maybe sometimes the goo will collect a whole bunch of material - maybe hundreds of tons or more - and fuse it together into gigantic super brains of inconceivable intellect. Maybe it creates hundreds of different morphologies and forms of hosts (out of the mass it subverts and it's own mass), and tests the capabilities and efficiencies then shares the information collected with other goo nodes, who will catalog and note the most capable morphologies and ever improve upon them. Maybe the goo can even figure out how to make and communicate via some kind of biologically grown radio. It could probably grow all sorts of traits and features that may be impossible with natural evolution but are easily within reach of the design of this thing.
And when it faces some new challenge or threat, it may be able to rapdily reconstitue (as in over hours and days) it's mass into more useful forms for whatever it requires. It might be able to get millions of years of evolution done in days. A rapidly evolving, subversive, and collective hyper-intelligence.
This may unironically be the ultimate form of biological civilisation if it's at all possible, and would probably be something that could eat the Necromorphs alive even with their thermodynamics ignoring bodies.

>>16943168
>>16943189
So the Flood?

>>16943286
The Flood are a bunch of incompetent losers despite being even more space magic than the Necromorphs. If Master Chief tried to fight this thing he's dead in minutes at best. It's not that hard, just send a couple multi-ton armoured superintelligent organisms with muscles several times stronger than an elephant's pound for pound, an absurd reaction time thanks to nerves that process information faster than a Penaeidae shrimp (which is already three times faster than a human), and have redundant and distributed biological systems so some pitiful rifle fire isn't having an easy time killing them. Have them linked and coordinated by biological radio (looked it up - biological radio is likely possible from a physics perspective), and have thousands of smaller organisms - ranging from dog-sized to bacteria-sized - attack and degrade at his suit as he fights these.

>>16943168
The bio threads are because of Heil Mary

I think they'd just boil from the ridiculously fast metabolic reactions