I could do that myself now: make a copy of core, change the PoW formula, and presto: a hard fork happened, and the coin has split. If the 1000 PH/s is not important, what is the difference between my bitcoin and their bitcoin?
For a start, the PoW.
After that, it depends.
Depends on what? If the hashpower is not important, and preserving the PoW is not important, then what is the magic factor that would cause all the value to go to the CoreCoin branch instead of the CartelCoin branch?
Whatever it is that the economic majority thinks is more important. If it is sticking with the existing miner fleet, that's where the value ends up. If it is firing the existing miner fleet, that's where the value ends up. There is no answer you or I can state without that information that is more correct than another.
ELI5 the mechanism for the the "economic majority" to make its wishes known & relevant?
The market.
Assuming I hold 90% of all the coins mined to date (I'm economic majority), how do I go about this shit?
If you own 90% of the coins, you are the market. Obviously not realistic. In reality there are many participants, and they'll trade with one another and work it out. One fork will be worth more than the other, probably a lot more, but who knows.
90% was chosen at random. Let's say I own 5%, and keep in in cold storage, as a "store of value." How do I make my voice count?
Keep in mind, you edited out the important part:
<>If I'm just holding the coin (not solding), why do my wishes matter to the miners (I do not buy, only hodl)? To the exchanges (I do not trade, only hodl)?
According to your reasoning, by not trading (hodling the coin in cold storage), I effectively make myself irrelevant. Correct?
What happened to the "store of value" function? To store (and be considered a part of the "economic majority), I must buy & sell?