Summary: It gets very annoying when I have a favorite mod and it gets outdated and I can no longer use it once minecraft updates. It will allow mod makers to focus more on bug fixing a new features rather than working on getting their mod updated.
Description: Mods won't need updates when minecraft gets updated, only when the API gets updated.
Proposed Addition: Older mods still work with new minecraft versions
Justification and Use Case:
This would allow mod makers to focus more on mod features and fixing bugs. example: Im using a minecraft mod 1.5.2 on minecraft 1.6.2 minecraft