Most of all, I expect the crafting system to be about an alternate means to obtain troops currently available with key pulls and not some other exclusive pool. Anything less would be extremely disingenuous to the initial pre-announcement made during the guild wars wrap up. It needs to make collections completable again, normalize the cost of new troops, and stabilize the gem economy somewhat. Inflation on gems (the decrease in value of what any given number of gems will "buy" you) has gotten out of control and continues to worsen for both individual players as they collect more troops as well as with game age as more troops are introduced.
I hope that when I want to craft something, the "new game mode" doesn't dominate my gameplay time while I'm doing so. Ideally, it won't be overly disruptive to my routine and I can continue playing the core game while making other decisions that steer me toward completing a craft (which kingdoms to explore, which troops to hunt down, whether or not to use soul generators etc).
I hope that whatever the new game mode is uses your progress and collections. Many people (including myself) would not be too keen on a "Treasure Hunt 2.0", but would grudgingly play it anyway if it was the only reliable way to unlock certain troops.
I hope all troops are craftable, including Guild Wars troops, finally moving Guild Wars into the "actually optional" column.
I expect there to be a time lock/premium component (force waits, gems) and/or an RNG component (please god no) to crafting in addition to the effort component (farmable stuff like traitstones or souls or monster parts, basically anything you'd have to go and collect yourself).
I hope effort components to be the main deciding factor on your ability to accrue crafting components, but I expect the opposite to be true.
I expect there to be a purchase component to accelerate crafting, but not a required one. I'm fine with this, so long as the in-game costs without the accelerator are resonable.
I hope to see a preview of the system within the next month. I expect to see one before 2018. I wish the next update was actually about crafting, but I suppose the Unity port, fixes, and QoL issues were higher priority. I hope it doesn't break too much stuff..