Okay so the new patch is out, and so far it is interesting. What's been added, as the patch notes say, are premium fusion slots and enchanting for mythics.
For the premium slots, the slots start at 1000 gems, and get progressively more expensive. On discord we have come to the conclusion that the value of an item is a major factor in which item is used as a duplicate. That is great when fusing similar items, but the downside is that it does prevent 5 item fusions, at least until a toggle button is implemented(not a feature being worked on, AFAIK)
The mythic enchanting has it's own button, and it's main function is to fuse several myths together to increase the ranking of the item. The ranked item is still sellable, but I am not sure if the value also increases. Also, just like with fusing leg to myth, filling up the cauldron will only give a partial success rate. It's clearly intended to be a whale mechanic, but might make lower level myths have some extra value.
Now as for the class items. No, the pack items are not having their skill changed to mythic. In fact, the only changes are to the Ninja class, where Valkyre's Embrace is now Amazon II instead of Wise II. The Loki's Mask is now Treasure Hunter III on Legendary instead of Arch Wizard II on Epic. Finally, what is being changed to mythic are the low level items that come with the pack.