First of all I have to admit I am a pessimist practical person. So if I tell the idea is feasible you should accept it
The fact that you wrote me such a long answer denotes that even you hope for human prosperity. we all know how poisoned the system is and how hard will be changes, but we have to cope with it or just sit and wait for things getting worse until die.
I prefer to “act”.

lets try to solve issues one by one.
You may heard “code is law”. Once we transformed our “good” rules and mechanisms to code and run our servers, the law will govern forever. Our good and fair law will dominant and defeat old mentality, like all “old mentalities” we missed because of technology dominant. This is the place that gradual changes takes place.

The Bitcoin “started for the good purpose and ended up being another speculative asset”. That’s true because it was first experience and Satoshi missed some points about its game theory. It doesn’t mean Bitcoin is must be the last experience. We can create a new better one. In fact we have to create a new one, to appreciate the idea of having center-less monetary system. We have to enrich this idea and enhance it to center-less governing as well. And we have to foreseen challenges. After one decade we are far mature than early Cypherpunks. aren't we?

"As long as there's a living system - be it human organized system, monetary system or something else - there's going to be decreasing entropy, thus increasing centralization over time."
That is true. The better way to say it is, all systems can tolerate a degree of entropy. If the entropy exceeds the tolerated level the system will collapse. Additionally all systems (either an organic system or a human organized system) tend to decrease entropy in order to increase its live.
So we have to follow these strategies.
1. design a system that tolerate maximum level of entropy and decentralization.
2. design more than one system simultaneously.  The systems are working independent and in parallel.
3. make it easy for people to enter and exit different systems with “no cost”.
4. the entire ecosystem (all different systems with different level of entropy and decentralization tolerate) enjoys the power of fragility and hardened by this fragility.
5. the last but not the least, at least one of these systems must start from super centralized structure and moves toward super decentralized system. This particular system is the backbone of the whole ecosystem. Day by day this system is more decentralized while the other systems can move toward more centralization or more decentralization.

"people will end up gaming any system and eventually even one single individual will either find benefit to cheat the system, or entirely out of craziness (as you said there are possible tools to motivate even bad actors to act good by benefiting them) will try to revenge against the new decentralized system and fill find supporters with enough brainwashing power, thus just again - increasing centralization."
Thanks for your insight and predicting these scenarios. So we have to deal with. That’s why we have to design more than one system simultaneously, and that’s why people must be able to enter and leave systems with no cost and that’s why the entire ecosystem is hardened by this “fragility”.
People will be free to enter a system (accept a money) or leave a system (do not validate that money) with less cost. The insight is, the weak game theories or insecure protocols or corrupted societies, or cheating monies must be destroyed as soon as possible. Before their money obtains a fake price, before they scam average people and before they accomplish the fraud, their money and their community will be disgraced. It is “the power of fragility”. Meanwhile the honest communities and coins will grownup and increase their population (believers) and raise up the value of their coins.

The idea of “new system with credit" context isn’t new and as you mentioned, they examined it before in different places and different times. Some of them were too successful and some failed. We already have different kind of “mutual” systems, reciprocate, parecon, time banks as well. We have also many local currencies -whole the glob- that are in action actually.
BTW what they are all missed is they are bind to a limited Geo-location and have narrow market and they are all suffer from high centralized administration, since all are created before internet era. Some of our systems can pick the best part of them and armed them with decentralized protocol. In such a case the adversaries can't stop them.

If we put enough incentives in our systems, people will abandon their common thinking, beliefs, history, norms, and systems and simply adapt to the new paradigm.