The gimmick has run its course, the monster magic is gone; Glen ain't a monster; he's just some old dude, dude. Dave Meltzer said on Observer Radio a few months ago that Kane had requested his retirement a year ago, but Vince asked him to stay on a little longer for some reason; so I'd expect him to be gone within two years to be honest.
he should feud one last time against the undertaker. undertaker burns him and he returns as an mysterious supposedly burned masked character. something like that could bring the old kane back. its very hard to bring that mystique back that sorrounded kane in his original run