Should a maximum time frame be set of how long an Expiration date can be?

If Ransom does not set a time limit, (say 14 years, or something reasonable like that), then bad Holders may try to set really Expirations like 30, 40, or even 70 years, effectively making the Expiration date pointless.

But is this really a serious threat? Does the Ransom model itself actually need to set this, or can we let the free market manage this?