If you look at the lore linked in the doc, Triffids and fungus ALREADY live in harmony (under the complete domination of the Triffid Heart, which functionally suppresses the spread of the fungus and its natural inclinations but uses it as a symbiote in limited capacity), and the Triffid will be more than happy to live in harmony with the humans as well! (So long as it has complete control over them and can find a use for them within the collective, the same way the earth trees live in harmony with the Triffids! The Triffids are just so inclusive and welcoming, so long as those it is welcoming are completely subjugated and their free will entirely subsumed!)
It is NOT living in harmony with the wild uncontrolled feral barbarian-like fungus colonies, though.
But this probably belongs in the lore threads discussions in the Library, the official threads there are a good resource, although everything in them is, of course, susceptible to change should we decide it better fits the design goals of the above document to change things, especially things that aren't actually implemented yet.