Mechanics cannot, game terms and specific wording can. It's why no other game but Magic: the Gathering can use 'tap' as a game term to describe rotating your card 90º to one side. The basic Power block, for exemple, is probably a specific design element you can't copy, same for all the keywords.I don't quite understand why this cannot be done. Game mechanics cannot really be copyrighted.
The 4e game licence was basically crafted specifically to avoid a Pathfinder situation.
It wouldn't be easy for people to use their existing 4e collection and you wouldn't be able to lean on it for content. You'd have to basically rebuild EVERYTHING from scratch, which would mean a LOT of work for a indy company. It's just not a realistic proposal.