Well, it's hard to estimate the coins lost so we don't know how many of them currently circulate. Anyway, I'm just interested in _possibility_ of such reclaiming, I don't insist it should be done in the software in any way. Just in theory, can we somehow check when the particular coin was spent last time? If yes, then if (when) in future we'll have too few coins left, there will be a way to reclaim that were lost. The timestamps are stored in blocks, AFAIK, so it may be possible. The check period may be a year or so, if you didn't run your client within a year at least once, your wealth will be treated as lost. To confirm your ownership you can (for example) make a transaction to the special address that won't be counted but accepted as pong. As it will be done once a year, it won't overload the network. Will this scenario potentially work or I completely misunderstand some principles?
It's not really necessary. Each coin right now is divisible into 100 000 000 parts, so in reality we have 2 100 000 000 000 000 (2.1 quadrillion) coins. Even with a total value of 10 billion dollars, the smallest part is only worth 0.0004762 of a cent. Even if we lose 99.99% of all coins (a heck of a feat), then the smallest part will be worth 4.762 cents. A loss of resolution, to be sure, but not the end of the world. There is already talk of extending the precision which would make this problem moot.
There is also no need for us to "know" whether the coins are lost or not. My problem with the whole idea of "checking ownership" is that it's exactly the type of feature that could be open for abuse. In any cash system, people should be able to hold on to their cash for as long as they wish without worrying about whether the system will yank their coins out from under them. Losing coins or not spending them has the same effect on supply and demand. Imagine if you had a ton of gold and either buried it in the ground or dropped it into the ocean in the middle of the sea. You are removing that gold from circulation. It has the same effect on supply and demand, so long as you don't pretend you still have the gold and use it as collateral or make loans based on it