I like the idea of only having 21 million bitcoins.
Bitcoins get lost all the time, lost private keys.
In time we will have fewer and fewer bitcoins, currently it is thought 3-4 million bitcoins are already lost. This makes me sad.

I think this is part of the design of Satoshi, same as bitcoin transaction is irreversible, so why change it?

I propose a redistribution method:
>If an address did not have any activity in let's say the last 100 years the address is considered lost and the bitcoins are free to be mined in the next block.

To prevent losing your bitcoins you make sure to transfer them to a new address every 100 years (I am not aware of any other method of "proving" you still have access to an address).

P.S. This would be a change in the consensus mechanism, I know 
P.S.S. I am aware of Satoshi's view on this "lost coins are a donation to everyone". Yes, but 4 million is a lot, do we want Bitcoin to still be used 1000 years from now? If this trend continues most if not all bitcoins would have been lost by then.