After a long hiatus from this type of topic, I have returned. But far from being a charged rant, I will deal with the issue at hand as a carefully controlled inquiry. And what, exactly, will I be inquiring?
The intended relationship and handing off of the Mantle from the Forerunners to the Humans, and what exactly the Forerunner intended beyond what we already know. The other part of it is how this is meant to involve the other inhabitants of the galaxy, the Halo Array, and the detritus of Forerunner civilization that everyone but the "Reclaimers" have access to.
To begin, let's do a quick recap of the relevant information. The Forerunners index and catalogue the species that the Array would affect, and stumble upon Humanity, who are somehow connected or related to them and are special, enough so that the Forerunners designate the Humans as their successors and holders of the Mantle, the religion that calls for the cultivation, protection, conservation, and prospering of the galaxy's ecologies and civilizations. After the Array fires, the Flood defeated, and most of the Forerunners and other sentients except for those indexed are destroyed, the remaining Forerunners and their automated mechanisms go about the tasks of reseeding and reestablishing the galactic ecology before they depart from the galaxy in a march, voyage, or "Great Journey" of shame and guilt, never to be seen here again.
And here we approach the main problem; each indexed species is returned home and allowed to repopulate and rebuild on their own, except for one thing; almost every world reseeded and otherwise is carpeted in Forerunner installations, artifacts, records, and technologies. So many worlds are like this except for perhaps the most important of all, Earth, the homeworld of the chosen race, the inheritors, the Mantle holders, the Reclaimers. The only serious artifacts there are a portal to the Ark and attendant facilities, with perhaps others sprinkled here and there, such as the Pacific Ocean floor and Mount Erebus in Antarctica.
To add further complications, at least one race, the San'Shyuum, develops further than anyone else, accesses, uses, and gains control of Forerunner technology, creates a fearsome religion, and proceeds to rampage across the Orion's Arm of the Milky Way, allying with the Sangheili, and establishing the ferocious Covenant that we know today. This is a prime example of the biggest problem with the Forerunner plan regarding the Reclaimers: how they are to gain their designated inheritance, enact their chosen role, and do so when they have no way to acquire and access it, while every other race in the galaxy is given free reign and easy access to the Reclaimer's inheritance.
What then, was the Forerunner's plan? Did they want Humanity to develop on their own without Foreruner influence, make contact with their neighbors, locate their inheritance, communicate, make treatises, and create some sort of "harmonious" coalition based on the Mantle, everything would work for itself? Or was there a genuine plan for the Reclaimers to get what they needed before things got out of control, either from the formation of a Covenant-like organization, a Flood outbreak, or some other issue, but was not enacted for unknown reasons?
Why would the Forerunners make so many efforts to right their wrongs, restore the galactic ecology, select their successors, but do nothing to ensure that the Mantle is corrected, reinstituted, and a proper galactic society is formed? Its as if they expected everything to go perfectly without a hitch, and that everyone would be able to get along regardless of divisive sociopolitical, economic, and territorial issues, especially with the knowledge of one species, Humanity, being favored above all others. Such a dichotomy between Humanity and the rest of the galaxy is all but asking for trouble, for Humanity has by proxy of their position, authority and eminence over every other life form in the galaxy, and with the Mantle and their status as witness, they would be able to decree and design how everyone else is supposed to live.
Do you see where this is going? First Contact between educated and enabled Reclaimers and their designated charges/subjects would easily lend itself to conflict and war, for there would be too many things that could go wrong, such as the other species refusing to accept the institution of the Mantle over them, religions and cultures based on Forerunner artifacts, and issues such as a desire for power, sovereignty, and free-reign without interferrence would appear very quickly.
In the end, it could result in the Flood being released, the Array fired, and the galaxy being rendered lifeless, or fully succumbing to war and the Flood. So how might this be addressed?
That we will approach below.
____Part III: Conclusion___________________________________________
In order for the Reclaimers to do what they were meant to do, perhaps the Forerunners should have stayed around longer, carefully raised, trained, and groomed the Humans for their role, while at the same time ensuring that there were not too many installations, records, artifacts, etc. for anyone, Reclaimers or otherwise, to abuse. After the Forerunners start this process and then depart, they could also have enacted various autonomous measures to help the galactic ecology and its designated overseers to develop and interact in an even-handed, fair, moralistic, but realist-minded way, and only truly intervene if things get out of control.
That way, if conflict does arise and galactic war, Flood outbreak, and Array activation looms, the Reclaimers and their charges will be able to come up with a way to salvage the situation, and a proper galactic civilization could then proceed into the future.
But the question still remains, even with this hypothetical scenario and solution, what the Forerunner's precise plan was, and what they intended for Humanity and the galaxy. Hopefully we will learn more about this in the future.