Bitcoin has no way of knowing if a given Bitcoin is "expired" or has a Base58 address that no one has a key for

One way of ensuring that coins are never lost is to expire coins and add them back to the coinbase at some future date. People with active keys would simply move all the coins to a new address within a 5 to 10 year period.

• Has anyone explored the pros or cons of this, how it impacts velocity of money?

A few benefits off the top of my head include

1. Forced upgrade of all coins to better newer technology (SCrypt, Sha512, etc)
2. Better analysis and less speculation of the network (coins in circulation is constant)
3. More incentives to mine after the 21 million BTC mark is reached

Note: I'm not proposing a change to Bitcoin, but want to see if any Alt-coins have researched this area.

Bitcoin has no way of knowing if a given Bitcoin is "expired" or has a Base58 address that no one has a key for

One way of ensuring that coins are never lost is to expire coins and add them back to the coinbase at some future date. People with active keys would simply move all the coins to a new address within a 5 to 10 year period.

• Has anyone explored the pros or cons of this, how it impacts velocity of money?

A few benefits off the top of my head include

1. Forced upgrade of all coins to better newer technology (SCrypt, Sha512, etc)
2. Better analysis and less speculation of the network (coins in circulation is constant)
3. More incentives to mine after the 21 million BTC mark is reached

Note: I'm not proposing a change to Bitcoin, but want to see if any Alt-coins have researched this area.