Have been away for a bit but back now so will address. To begin on the subject of discount-SMs
Can we make psuedo-marines a viable option in our forces?
Alternatively, if that sort of thing is currently completely unacceptable/unviable given we have contacts with both the sororitas(who use such)and the mechanicus(who likely have experience making such) could we have human-sized suits of power armor commissioned for them so that they could serve as elite leaders (or rather be nudged towards being leaders) amongst our mortal troops at least?
A space marine is more than merely their body, they a mix of tech like power armour, their biology, but also importantly their training and indoctrination. The Imperium possesses these various things in different measures, for example, yea, maybe a Karaphron Breacher or other high end battle servitor has similar strength or resilience to a space marine, but it doesn't have the training etc so it would still lose in a fight. A Soroitas has the same training and and resilience (or near enough not to matter much), but doesn't have the training, equipment, or 'quality' of a space marine. In short, what makes them so great and so effective as warriors is that they're high quality, they're the highest quality thing the Imperium can produce at sufficient scale to actually deploy units of them. Now sure some Magos could make a murder-servitor of exceptional quality, but that's not a process, that's a 'bespoke' thing where they'd have to make them one at a time, whereas the Astartes project is pretty consistent in results etc.
No one is going to do an Astartes' job as good as an Astartes. That's a pretty flat statement. You can come in and say 'oh but what about x' but its meant to be broad. I like the idea of 'improving' the process, that's why I drew the Rapid Zygote Maturation stuff from Huron, and why I lean on Badab in general with this quest.
I'd also say that while maybe the Imperium could do this, Space Marines wouldn't. I think I've mentioned it previously but I'd intend that if the Chapter was having resource problems they'd cannibalise the other bits of the Imperium-on-Mallus. I've alluded to this before:
In the absence of Apothecaries, the Scouts had turned to their own medicine, mutilating the crew members and serfs, harvesting their organs and sinews to try to substitute for the gene-seed they were to receive. The ship had eaten itself from the inside, and instead of warriors, Natohk faced great mounds of pulsating flesh, many with multiple arms crudely sewn on, their innards extruding from places where their skin couldn't contain them, entrails bursting out as if a perverse reflection of the breaching charges used to gain access to the ship.
However in your current state this shouldn't be necessary. My point is that because you chose to play Marines the Marines will put themselves first. It would be out of character for them to divert resources to make worse versions of themselves when there's not some urgent need for it, which there isn't.
I'm quite interested in how you'll look to 'improve' Astartes in general btw. As a short note on how you might do this, maybe enchant the Black Carapace bits, or replace them with that magic elf metal or something. Put a seed from the oak of ages in their chests instead of a second heart. Have them drink dragon blood, experiment to make not-Vampires (eg an elixir of life deal like with the original vamps), do some Stormcast Eternals stuff and make magic bodies to put their souls in, deploy magic items at scale, such as a Seeds of Rebirth, or Dwarf Runecraft stuff, all sorts of things really, put a rune of speed on a suit or terminator armour, make power armour out of gromril.
In general I'm pretty indulgent as a QM, so if you did some of this I'd be inclined to make it interesting rather than just saying 'Brother so and so drank the dragon blood and nothing happened'.
Anyway, I think that's addressed, but to move to the wider point
So TLDR for this later segment: Maybe Its a bad plan but do you or anyone else have a better one right now? I'd love hear it if so.
It's fine I won't pretend to be a military or civil engineering expert at all.
I certainly don't require people to be experts, that would be pretty silly, and I'm happy to take ideas rather than specific plans.
Essentially, as I've mentioned before, what is the problem you are trying to solve?
If your marines are dying lots then.... get other weapons? You have 3 titans and an airforce. You have thousands of techpriests, you have Magi and Techmarines. Build a Valkyrie factory, build a gun and artillery factory, build a tank factory, build a chemical weapons factory.
Actually uplift people. You haven't done this yet. Yes there's been other stuff to do, sure, but that something you need to do if you want to get more dudes to fight your battles. Imagine a Mallus where every village has a store of small arms and a wall. Guns will deal with any heretics or rebels, who wouldn't hvae access to such things, imagine militias ready to be called up for temporary service. Oh, a Beastherd has been gathering over there? Call out the regional militia, reinforce them with some artillery or air assets from the local PDF garrison. Oh the herd is too big? Ok get the actual PDF over here with their tanks and bigger artillery, flatten the Beastmen camp with artillery, move in and blast that Minotaur with the cannon on your tank. Drive your Hellhound down into that Skaven warren or goblin nest and flame them all, then move in with shotguns and submachine guns. Oh there's a lot more of them? Better deploy the machine guns and keep them well fed with ammo! But wait, something else is going on, well the air force is here, conduct a bombing campaign, call in the Lion Guard, the best of the PDF from their base further away. They arrive on trains or ships in ports with facilities for massive cargo vessels which make trade and distribution of resources far easier. Watch as stormtroopers with carapace armour and hotshot lasguns blast apart those daemons which seemed to have been forming, and the Daughters of Elayra, the subverted Sororitas, march in with their power armour and bolters. Something even worse is happening? Call in the Space Marines ,drop pod assault from orbital assets, Thunderhawks setting down tanks, and if necessary, a cargo lander delivering a God Machine and it's attendant Knight-Armingers. Then when it's all over finish up with a gas bombing from air and artillery and make sure any surviving xenos/heretics/mutants cough up their lungs from wherever they're hiding.
My point in this is that the Marines should be a last resort. You don't really need shock troops. You need a lot of guns and a reasonably well trained professional force to use them, backed up with a large reserve and militia. Yes, there will be problems with this, risks, issues, and so on, but you've chosen in that vote a while ago to uplift, so this is what an unlifted world looks like. There are millions of humans on Mallus, arm them. Astartes are cool but there's loads of planets, even death worlds, which get on fine without them.
I ask what your objective is because the vast majority of Mallusians are subsisdence farmers. There's this enormous untapped resource you've got which if you uplifted people you can use. Modern farming techniques mean that most people aren't farmers etc, and that farming is done with a lot of chemicals etc. Even if you went for a less efficient slash and burn type of farming, you have the whole continent of the Southlands almost iwth its jungles to do that in, so efficient land use isn't actually that big of a problem.
Now yea, if you really want, you could have a chat with the mermaids. Ok, sure, how many are there on the planet? At most, shall we say a million? There's got to be 100m normal humans.