If standard foot platoons were a hazard in maps like Urban or Lowlands? (You know, where you'd expect to find them...) I'd be intrigued. But, well, the best ideas I can come up with are basically functioning as 'mobile weapons emplacements' which aren't dangerous except to already-damaged 'Mechs . . . and could be avoided once noticed.
Not to mention...What would happen to infantry on a Tropical Biome. I don't know if I'd trust those 'spore' fields and clouds.
You want a zombie apocolypse? Because that is how you get a zombie apocolypse.
I've seen The Last of Us, spores and people don't end well.