You can bet Boeing was all for this. Twenty thousand cycles for 747. Fifty thousand hours or 50,000 cycles for a MD-80. The term is LoV -Limit of Validity.

"WASHINGTON, D.C. – In a continuing effort to address aging aircraft issues, the Federal Aviation Administration (FAA) has finalized a rule designed to protect most of today’s commercial planes and those designed in the future from structural damage as they age.
The new rule seeks to prevent “widespread fatigue damage” (WFD) by requiring aircraft manufacturers and certification applicants to establish a number of flight cycles or hours a plane can operate and be free from WFD without additional inspections for fatigue. Manufacturers have between 18 and 60 months to comply depending on the particular aircraft type.
Once manufacturers establish these limits, operators of affected aircraft must incorporate them into their maintenance programs within 30 to 72 months, depending on the model of aircraft. After the limit is in the maintenance program, operators cannot fly the aircraft beyond that point unless the FAA approves an extension of the limit. "

The link to the rule is here:

http://www.ofr.gov/OFRUpload/OFRData/2010-28363_PI.pdf

Amazing that the Feds wasted the paper to explain that they included stuff like Comets, the Concorde and Whitworth Argosy because, while no one is operating them under 121 presently, they wanted to be ready in case someone resurrected one in the future.