i should add that definitely a lot of older ones with less grunt won't be because not all SHA256 altcoins had 80 byte long block headers

many of them sit idle, uneconomic as anything but a resistave heat element in all seriousness, but this could spawn a new value to chase with them

Proof of Work: leave it to the bitcoin chain and forget any other use of it

the economics of proof of work are like bitcoin itself: there can be only one

more than one target to use it on and the hashpower will dance the tango on your protocol