The answer shouldn't be rewarding players who completed the original grind, it should be about making the "new" grind be as difficult (roughly) as the old. To me there is no easier way to do this than to let Lorekeeper Lydros accept Libram turnins. He's still in Dire Maul, his gossip text still actually recognises whether you completed "Elven Legends" or not so why not just put the quests back in? Hell they could've avoided the whole disaster if they'd just lied and said "Whoops, we didn't realise that we'd taken the Libram quests out, they're back in now though"