During the most recent Developer Update Livestream, it was confirmed that Uber Duriel will continue to be the best option for players who are looking to target-farm Uber Unique items during Season of the Construct.
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While there will be a new boss fight in Uber Malphas, the developers elected to not tie him into the current boss ladder that has existed since Season of Blood. Instead, Malphas will have a chance to drop Uber Seneschal Stones, and players will still need to grind out boss summoning materials in order to work their way up to Duriel for their best shot at the build-defining Uber Unique items.
The boss ladder was first introduced in Season 2 so that players could target-farm Unique items.
While it was known that this iteration of the boss ladder would become a permanent part of Diablo 4, some players have been hoping that there would be additional avenues for target-farming Uber Uniques.