1. What if miners start sabotaging block creation after 2140? Would introducing some coins that haven't moved since January 2009 help? (Similarly, in four years, in 2144, coins untouched since February 2009 could be put into circulation, and so on.)
2. Some say quantum computers could crack private keys of UTXOs created in Satoshi's time. By the time such computers exist, nobody will be using the old algorithms (the community will be forced to transition to something else). But would it be fair that the UTXOs from 2009 go to the quantum computer developer? Wouldn't it be better to change the consensus regarding UTXOs made with old algorithms when transitioning to new ones?
1. There is nothing to suggest that miners will sabotage the network after a certain date nor do I understand what you mean by sabotage.
Forcefully accessing coins that are stored securely in wallets is not a long term solution to any issue Bitcoin has or might have in the future, but it is a short term way to break trust people have in the network.
2. If there is a network transition, it affects all bitcoins stored on it.
except in cases where vulnerabilities are discovered on individual wallets used to access the private keys.
In the year 2140 we start stealing the coins which have been not moved since January 2009.
In the year 2144 we start stealing the coins which have been not moved since February 2009.
...
In the year 8428 we start stealing the coins which have been not moved since January 2140.
...
If the network has survived a hundred years without those coins moving, it is not necessary for the future of bitcoin. There is no upside to a decision like this and it not a problem we will have to face in our lifetime.
- Jay -