Never is a long time.  Still even without quantum computers if a flaw is eventually discovered that degrades the security of ECDSA, coins may eventually be "recovered" with sufficient amount of computing power. 

I think you are missing the point.  If ECDSA is degraded we likely will see a hard fork which introduces a new "higher security" address.  A lot of users will move their coins, some may not, and those who addresses where the private key is lost can't be moved.  In time the academic vulnerability will become economically viable and the unmoved addresses will be cracked and the coins "recovered".

The timeline might be measured in decades, you might not even see it before you die but never is a long time and it is at least probable that on a long enough timeline it will happen.

Okay:
Bitcoin is only a few years old - we have no idea what it will be in 50 years or even in 5 years, but the lost coins aren't hurting anyone except the person who lost them.  They actually benefit everyone else by reducing the supply, and thus supporting BTC's value.

i never said return to owner. the lost $100 bill is either picked up by someone else or printed.
there is nothing wrong with 21 mil coins being out there in total and that putting lost coins into miners blocks is a good thing actually

miners are good for the bitcoin protocol - without them your bitcoins would be worth close to 0

coins that' haven't moved for say 50 years ARE lost coins. by nature.

Not on "my Bitcoin network" and you need a consensus of users to make a hard fork.  It is a bad idea, and it will never happen, but that doesn't mean someone discovers it as a "new" idea every other week.

how so? makes no sense- someone picks that $100 up - point lost....

please tell me why recirculating coins that haven't been moved in 50 years is a bad idea? logically please. (i propose a blacklist based solely on time, nothing less and nothing more)

Bitcoin is a social contract. People value it because they trust it.  People adopted it knowing the "rules".   One of those rules is that transactions are irreversible and stealing the output of a transaction AFTER THE FACT is theft.  Pure and simple.   You can justify it, you can rationalize it but it is theft.   If the Bitcoin social contract is broken, people won't trust it and when they don't trust it the value or utility will fails.   

Furthermore even if it WAS a good idea 50 years (artificially chosen by you to make the idea more paletable) is just silly.  If Bitcoin can exist and even thrive without redistribution for 50 years why would it suddenly need it after 51 years.  The reality is it won't.  So the 50 years will probably someday become 30 years or 20 years, or 10 years.   The more people start changing the rules after the fact the more confidence that will be lost in Bitcoin.  If you can change the "transactions are irreversible rule" why not also change the number of coins that are minted rule, or maybe help the governments of the world and change the nobody can stop/prevent/block transactions rule or the users are psuedo anonymous rule.

For this reason it doesn't matter how wonder you believe the idea is many people will never accept it and many who may be neuatral on it will never support a hard fork with anything less than near unanimous support for the massive chaos and value destruction such an event would cause.

Now if you start an altcoin which has a x year use it or lose it provision I still think it is a dubious idea but you have created it up front.  If users adopt that currency they know (or should know) the rules up front and there is no ex post facto change.

They rise to Walhalla into wallets of those killed in battles with honor. The great warriors can then buy vodka and hookers for these bitcoins.

[joke mode off]
Actually, some demurrage would be very useful for bitcoin. Something like 5% of wallet balance plus 1mBTC per year. This would cost nearly no loss for hoarders, since bitcoins appreciate in value by 1000% per year, but it would return lost bitcoins back to miners with time.
[/joke mode on]