Not a fan of what they have shown on paper for Tempering, as is, and I think it needs work. I think RNG on top of RNG is not good overall. There should be a more deterministic way of putting the affixes you want on an item.
I think they should have the new manuals drop with a random affix recipe on it (+ to Int or + to mana pool, etc.), and then you hunt items that match the item you want to temper. Crafting them would put that specific affix on your item. If you want RNG, you can put it there, with the quality of the affix, maybe being affected by the quality of the item you are using to craft with.
You could be using Rares as an ingredient in this way, to make them useful in the game. Allowing the manuals to be tradeable would also be good, as then people will want different ones, depending on their class build.
Overall, the idea would look like:
Find the item you want to temper (say a bow)
Find the manual you want with the affix you want. (With plus to attack speed)
Find a rare item that matches your target. (A rare bow that is the same base item)
Temper them to get item you want with the affix you want. (Bow with plus to attack speed randomized from 1 to 3).
This way you have some control over what you are going to get, and you can still have a useable item. As it is, you can brick your hard found “perfect” item easily, as you only have 5 chances to get a pair of random affixes you want on it.
Not a fan of the Pit being used as a farming spot for materials as well just for the new Masterwork system. I don’t understand why they need a new material. Why not use Gems? The better the gem, the better the masterwork chance and such, maybe certain kinds of gems will give you a better chance on hitting certain affixes?
As it is, The Pit is just going to be like Nightmare Dungeons, where you are in there for a specific reason only, rather than play how you want. Limiting resources to specific areas of the game is what is really frustrating about Diablo IV, as well as farming materials to unlock something for a chance at getting something then do it again.
Hopefully the Pit will be interesting, as that seems to really be the only spot people will be playing in in the end.