you can't do that without a hard fork because you are introducing a new rule in the system that didn't exist before. bitcoin is just a set of rules that need to be satisfied, when you want to remove a rule or add a new one, you need to perform a hard fork. in this case what you call "token swap" needs introduction of a new set of rules hence needs a hard fork.
those altcoins that are doing it already have that rule!

as for the process itself, even if 100 years pass you still can not call any of the  coins that have not moved "lost". maybe some line of family is HODLing bitcoin like that. you can not prevent it and you certainly can not force people to move their coins. for instance i started with bitcoin in 2014, today after 4 years i have coins that i have not touched for 4 years. you can't force me to move my coins because you think not moving is equal to being lost. i won't follow that bitcoin with that kind of "rule" in it.