What I would do is revamp Nebulites altogether. If we're not going to get AO, Nexon might as well make it that Jewelists can craft special Nebulites (I call them Master Craftsman's/Meister's Nebulites) that can give higher ranked Nebulites at a much higher rate than Nebulite Boxes. I'd also like to revamp the Galacto-Drill boss, but that's a topic for another time.
For Nebulites, I would do the following: 1. Remove all D-rank Nebulites, and make S-rank Nebulites accessible. Nebulite Boxes would only give C and B rank, while C, B, and A would come from Master Craftsman, and C, B, A, and S would come from Meister. 2. Create the special nebulites mentioned above and make them drop from bosses like cubes, as well as having fragments drop from elite mobs, bosses, and legendary herbs. The rates of getting good Nebulites would probably be similar to rank-up rates from Smithing cubes. 3. Make it that you don't need a Nebulite Diffuser to replace a Nebulite, but allow for Diffusers to keep the Nebulite if they are to be used, instead of removing them completely. 4. Allow for easier access to Nebulite Fusion Tickets, maybe via daily quests.