The thing that defines it to be a Nash equilibrium: namely, a Nash equilibrium is such, that for any individual entity, deviating from the strategy that consists of the Nash equilibrium is less advantageous than keeping with it. So once a system is in a Nash equilibrium, no individual entity has any incentive to leave it if it acts alone without collusion.
A Nash Equilibruim suggests there are different strategy profiles. In the context you present there are only ONE set of players, the miners.
Yes, you are right, the system is more complex, and there are also the users (people buying and selling coins essentially). But the Nash equilibrium is essentially this one, where the miners can only stick to the original protocol, and the users need to follow the miners.
In such an equilibrium, a single user not following the miner consensus is simply not going to be able to transact or to receive transactions: there's only one chain out there and he doesn't want to use it. And in the same way, a single miner forking away, without other miners following him, or other users following him, is a losing proposition.
Of course, this equilibrium can be broken, which is exactly the case of "forking away" and hoping for success in the market, but it needs a form of collusion between certain miners, and enough users.
As I said many times, this is a NATURAL way of evolving crypto: forking away, taking the risk in the market. With a PoW coin, this has to be initiated by miners.
Well, if miners adopted it, there would be not much choice but to follow along or leave your holdings for what it is.
What else could you do ? There's only one chain out there, your holdings are on it, and it gives 1000 BTC block reward. What are you going to do ?
Pray tell me sir how economic actors weight the value of the coins they purchase and whether or not the monetary base has not been inflated to oblivion?
Economic actors do technical analysis on coinmarketcap, or use any other betting strategy. The debasement is never part of these considerations apart psychologically maybe. The market price includes already all debasement. Of course, if you have some inner knowledge of WHEN these block rewards would hit the market, you might make a lot of money by shorting ; and as such, you've brought the information to the market. All information is included in the price. And secret information can indeed make you rich.