Disclaimer: I haven't used this yet, though it would have saved me a lot of time in the past.
This is a great idea which introduces one of Larry Wall's earlier great ideas to his latest brainwave. I'm sure many people have rolled their own ad hoc scripts to save themselves the trouble of manually copying/cutting and pasting the same diff recipe into a moving target, but this looks like a nice declarative interface which leverages other Perl power tools to get the job done in an impeccably lazy way.
Modules like Regexp::Fields, which ships a vast suite of separate patches, will probably benefit from this most in the short term. Long term, who knows? Maybe a metadiff (cf. Template::Generate), which figures out the metapatch from an arbitrary previous version to the current version and makes upgrades a snap?
The only drawback is that Template::Extract still has a few caveats and TODOs, and hasn't been updated for a while.