But services to keep track already exist. (But you have to be willing to pay for them, or else do the work yourself.)

All that doesn't exist yet is a way to have the service (rather than you manually) do something to extend the expiration (where it can be extended).

Note that not all programs allow you to extend miles/credits/whatever (in particular, many of the LCCs don't). In those, you have to get through a threshold by the "drop dead" date or it all goes poof.