Grade 5 has the same things as grade 4 anyway except for one or two new things. Mahogany trees for botany and gold ore for mining. That's pretty much it. Oh there's Dragon obsidian too for mining but that only exists because SE forgot to remove it when they removed things like darksteel and ebony.

So it stands to reason that grade 6 would have almost the same stuff as grade 5, just more of it with some new items. Tier 3 gems maybe (which do have recipes). They can add some new filler drops such as a new type of bone with recipes. Same with botany. It's easy to add new materials and give them recipes. They only need about half a dozen and the players will be happy just for the SP. They can still keep the meaty items like platinum, darksteel, ebony etc. for grade 7 or 8.