Adding new relic weapons most certainly won't happen. Mythics are job-specific (one for each job), Relics and Empyreans are type-specific (one for each weapon type). And since they didn't introduce any new weapon types with those jobs, i.e. there's already a relic weapon for each type, there's no reasoning behind adding more. If anything, they would add BLU to Excalibur, SCH to Claustrum, etc. And they have added new jobs on a lot of gear before, almost every weapon or piece of armor features one of the new jobs. Although at this point it might be a bit late, but it's still imaginable.