The game could definitely use a world merge right now, all they have to do is not to merge the most populated servers like Asura.
I play in Carbuncle and I like how chill the game is in here, we still get endgame done and help new players gear, the main problem here is the lack of materials in the AH but besides that I like it a lot better than when I was in Asura. If they merge those servers with under 300 players online I don't think that should be an issue, just a bit more competition for some abyssea NMs and bit longer queues for Ambuscade but we still wouldn't get the waiting times they got in Asura.