I think it'd be interesting if Spider-Man (or one of his clones) took a short stint as Captain America as a tribute to one of his/their heroes. It'd also be cool if a villain reformed and became Captain America for similar reasons. My first thought was Baron Zemo but I think it'd be a bit to awkward for a legacy Nazi to be Captain America. However I think the move in the comics was moreso to hedge the film franchise since Chris Evans intends to step down so they want to establish precedent for Falcon, who was just introduced in Captain America 2, taking up the shield going into Avengers 3 and beyond.