So there is no way crucible is going to become a permanent mechanic right?

Every recent league has been a test bed for some aspect of POE2. Crucible could be testing any or all of these:

-The idea of weapons trees
-Weapon trees and power creep
-Which nodes or types of nodes are most appealing
-Positive vs negative nodes
-Crucible monsters
-Crucible as a addition to Harvest
-Mechanics of the Forge of Titans
-Channeling mechanics of acquiring nodes
-etc.

Some of those might only be around for the league, others may be implemented in an entirely different manner in POE2. To test Weapon trees in a serious manner they had to create an entire league mechanic that may or may not be related to how they plan to implement them later. I suspect that is what happened with Ultimatum. They learned what they needed in the league and we will see it in POE2 in some probably new and different form. I think that we will see weapon trees again, but in some other setting.

If their game stats show wide acceptance of the concept then GGG will find a way (or already has a way) to add them to POE2. The crucible process may just be a temporary test masking the actual implementation.