Saying "nothing can really ossify it, not even after every block is mined" is confusing because if we were to stop mining blocks that would actually pretty solidly "ossify" bitcoin. It would also kill it. And it would mean no one is using it anymore.
But I don't think anyone is arguing that we should stop mining new blocks (well, maybe the feds...).
The ossification conversation is about bitcoin's consensus rules. There are some people who think that as it gets more complex and as it has more people using it, every change to the consensus rules introduces a large amount of risk (risk of accidental fork, risk of a bug, risk of introducing incentives that screw things up).
I have a lot of sympathy for this view. But I wanted to use Vitalik's post to think about how it might be a fool's errand to try to entirely avoid exposure to such risks by never changing the consensus rules again.
What do you think?
But I don't think anyone is arguing that we should stop mining new blocks
I didn't say that we should stop mining. I said 'after' means when 'there are no blocks left to mine, may be in 2141.
In that scenario, can Bitcoin ossify?
There will always be more blocks to mine as long as someone wants to mine them. If people stop mining blocks bitcoin ceases to exist.
Why would people mine when all 21 million Bitcoins are mined?
Transaction fees.
Think about this: how do you use bitcoin? How do you pay someone with it or receive it? A transaction has to get included in a new block.
If no new blocks are mined, no bitcoin can move. What is the use of a money that cannot change hands?