Making the Carbuncles interchangeable in the way that they did set a bad precedent, in my opinion. Now folks are going to expect, say, Shiva-egi to be able to handle all of the attacks of all three existing Egis, and that means designing attack animations for all of those different attacks. Doing this with Carbuncle was easy; the three colors are all pretty much the same model, so design an attack for one and you've done it for all of them.

I, too, fear that additional Egis glamours will be delayed or even canceled outright because of this, and the best we might be able to hope for are additional Carbuncle colors, like Aphinaud's Onyx Carbuncle, or Ulan's Diamond Carbuncle.