I agree with Callisto to an extent. The Excalibur isn't useful from the mage side of RDM, but it is incredibly good for soloing nonetheless.
I would love to see these new relics truly add things that made each job that utilized them stand out that much more via using them. The ancient idea of adding Relic Spells to them would be lovely.
I can just see the BLM now with their "Meteor" added spell. Or RDM with "Regain". Or a SMN with "Pheonix". I can't imagine, aside from song casting delay or songs + something or another, what BRD's would gain.
RNG I don't know enough about. BST maybe would get a special "Relic Pet" or CHR/Reward/Charm enhancements. WHM Cure Potency up with maybe "Holy II" or "Banishga III", but those would be somewhat worthless imo. (And I have Divine merits lol)
DRG may would get Wyvern enhancements and/or Jump enhancements. SAM more likely than not would / will most likely get things to do with Meditate, Third Eye, or Zanshin. DNC might would get a new Jig, Samba, Waltz or Flourish.
SCH I hope gets further enhancement of Light and Dark Arts and/or some kinda Relic spell. I.e. "Regain" or some spell that makes the weather effects add the stat for that weather as a bonus. (STR for Fire weather etc)
PLD should, imo, get that long wished for "Provoke" like JA. If not some adequate dmg reduction/enmity up stats. NIN should get Uts:San and maybe ninjitsu skill/tool expertise. WAR I also don't know well enough HL to think of anything it could benefit from.
THF might get a TH boost or enhanced steal capability as well as evasion boosts. COR might could get some kinda Relic Roll like... "Omega Roll" or something lol. DRK could gain enhanced drain / absorb spells and/or relic spell like "Ultima".
PUP might could gain Relic WS for themselves as well as their PUP with the obvious puppet enhancements. And BLU might could gain some kind of relic spell like "Immortal's Secret" or even a JA of the same nature.
All of which supposedly will all offer new ws which we can all hope might open up some further SC possibilities. Maybe even level 4 SC's to play with. Those are my thoughts on the possibilities. Who knows. All we can do is wait for the hackers to figure it out lol.
