I dunno.  

I think there's definitely a point about not wanting to suck in the bitcoin chain's uncertainty about how many coins are lost.  When someone explains to an investor that there's somebody out there who may have a million bitcoins - and nobody knows who it is or whether he's ever going to dump them on the market - And there's no way to keep track of who owns them now in case he's passed the keys on to, eg, members of his family who might have different ideas about what to do with them - The investor becomes understandably nervous.  It's like a large invisible hammer is hanging above the market, supported by nobody-knows-what.  

Maybe at some point Satoshi will need the money: perhaps he will decide he wants to retire on Mars.  And maybe not.  Maybe Satoshi will pass an inheritance to his niece, and she will decide she wants to buy Fox News.   And maybe not. And as much as 3 million other coins out there.... not held by any single pair of hands, but still nobody knows whether they are lost or whether the market will have to bear them.  

If I were to spin off an altchain, There'd just have to be a limit somewhere.  Whatever doesn't get claimed by a particular date ceases to exist in the altcoin chain, or it loses 20% of its value per year until claimed, or -- something -- just so that, at some point, we could write the unclaimed coins off the list and present a rational market where there's at least some idea what fraction is truly lost and what fraction is just in storage.