no they wont… you can’t buy any previous raid sets why would they start now? Even if they did(which they won’t) it would be a new currency just like they changed STV currency each phase so you couldn’t just hoard the old ones for the next phase rewards
Buying previous tier pieces didn’t just happened in Wrath Classic, it was like that in the original Wrath for catch up. But in Vanilla Classic and TBC Classic, they didn’t implement buying previous Tier pieces.
First, I do not think you will replace all 8 pieces of .5 Gear or Rank 10 PvP gear in your first visit to Onyxia, the World Bosses, or Molten Core.
Second, if you play a hybrid class with dual specialization, I doubt that you will be able to get Tier 1 gear in 2-3 roles in your first visit to the same.
They are invalid once you get better gear for that role in that slot, which is not guaranteed to loot drop, and until that point they are worth the time, particularly if you have three sets of gear to acquire for.
You know they’re unique 100 right? So even if they do add them to a vendor you can’t prefarm enough for a whole set (and lets be honest, phase 5 will have untarnished real’s and phase 6 will have glowing reals, etc so this is pointless regardless.)