Even ignoring the sanctity argument, the main reward for doing ultimates (I would argue- I don't do Ultimate's myself) is really the titles that come from the achievements. As demonstrated by the Blue Mage savage achievements it's not impossible to have separate achievements for parties of BLU- just have the original achievements not unlock if there are BLU in the party (and then separate BLU achievements and titles, just stick the word "blue" in there somewhere- "The Blue Legend")
But as I said, I'm not someone who does Ultimates but it's not just Ultimates they should be doing this with. All content of apropriate level should be doable with limited jobs as a way of bringing new life to that older content. We should be seeing BLU ultimate raids and BLU deep dungeons, and maybe even BLU exploration zones (althought I can understand why that might not happen- exploration zones thrive on massive populations and having separate instances for BLU's might not be worth it, and BLU's running around Bozja could ruin it for everyone else). Given that you can get BLU weapons from Criterio Savage, the fact that BLU will (based on what we've seen so far) never be allowed into Criterion Savage is ridiculous.
On the limit break point, I hope you're right. Dawntrail has been very "Final Fantasy IX" reference wise, so it is the time to give Blue Mages Frog Drop as their limit break (with LB2 and 3 dropping bigger frogs)