They went to +2 in FFXI so I have no doubt they'll add in +2 for Relics, maybe even beyond or other optional further upgrades for Relics.

Maybe there'll be completely different "legendary" weapons all-together that will require a way longer quest-chain that *might* keep the progression raiders who hate the fact that they aren't special snowflakes anymore from bitching because it'll be too easy for everyone else besides themselves to get it... who knows.