IMO it just doesn't make sense removing the progenoid glands. I really don't wanna see some silly shit like 'if the Apothecary removes progenoid glands from a SM corpse they will get some silly buff'.

I can understand why people want to incentivice it but none of the ideas so far have just screamed that's what should happen, the ideas while not bad feel like looking for a game play mechanic, the apothecaries are ensuring the survuvial of the chapter isn't that enough?

Honestly I think it should just be gain 50xp and no other bennifit. He's not a chaplain or a librarian so buffs are silly

Pretty much this. I don't mind seeing it represented as a trivial mechanic which offers minimal gain. But it really shouldn't be made into anything more than that

I've read (I think) that the Tyranids will be the npc on the battlefield during faction wars. I mean, you can be infected during the battle and if it success, lets say, during a specific time counter, you die and a npc tyranid will spawn. That's a unique way to keep them on the battlefield at all times. I mean, it'll be kinda fun with two factions just focusing fire on Tyranids until they're wiped out for a another time period(Orks and Ultramarines working together, heh.)

That's coming to saying that at the start of the battle, there will be a fixed amount of them. If you don't take care of them, they start putting pressure on both factions, so it forces your squad to think and handle multiple situation, it won't be much of run-and-gun. idk, I think it will be a great mechanic. And Apothecaries will be really useful then. And it would force to have more balanced class type in the squad.

Now, I know it will be really annoying to have this mechanic in every battle, so it will be only I guess, logical, to have it available where there the battle is held in an npc occupied map.

Two important facts you need to know.
A Space Marine has two Progenoid Glands. One is harvested upon maturity, by which time an Astartes will have become a full brother, so outside of the Space Wolves you don't harvest a scouts progenoids.

An Apothecary generally does three things on the battlefield, see to the injuries of his brother marines, if they are too badly injured ( half their brain gone, for example) he will administer the Emperor's Mercy, and he will harvest the gene seed of the dead.

So game-wise I suggest that he heals fellow SM, and can euthanize badly injured brothers so that they can respawn.

Harvesting geneseed does sound like an intriguing mechanic, with the aim of ensuring reinforcements at a later point, but it does sound like it would be better as some form of challenge (collect x-amount of geneseed) or as a narrative mission (Retrieve the geneseed of the dead and return it to base).

Also an apothecary does have the option of maintaining a badly injured Astartes life, instead of administering the Emperor's Mercy, so he can be interred in a Dreadnought's Sarcophagus. But this too sounds like a Narrative Mission.