(Pondered about the scope of this, as many other items could be included in regards to the Catalyst, but reading this reply about the similar Sandworn Relics convinced me to go with my initial impulse and limit this to Primalist gear. Also, ignore if you're already working on this, but I don't see this in the latest release or a related ticket)

When Patch 10.1.5 launches, we'll be able to convert the Primalist armor (anything "of Raging Tempests") to DF S1 Tier again, now with unlimited charges.
Upgrade levels 2/3 and 3/3 of Primalist armor correspond to the Normal and Heroic appearances, and converted items can be upgraded like Primalist gear to unlock the higher difficulty variant. edit: sadly, upgrade level 1/3 can not be used to get LFR appearances after all.

Hence, there is a lot that ATT could show here:

• On Primalist gear:
  • the Tier appearances for that slot of this and higher upgrade levels
  • when not fully upgraded, the appearance of the 3/3 variant, which uses the green Primalist recolor - Wowhead doesn't list the Raging Tempests items, but lookalikes: some items from rares, and unavailable epic items. (sidenote: this also applies to the weapons, if you wanna tackle those)
• On Primalist tokens: as they yield a 2/3 item, both the Primalist appearances and Normal & Heroic Tier.
• On S1 Tier items converted from Primalist gear: Tier appearances of higher difficulty.
• [Untapped Forbidden Knowledge] is used for the upgrade to 3/3, and already shows the green recolors, but should also include Heroic Tier items.
• For completion's sake, the currencies Elemental Overflow and Storm Sigil are used to purchase 1/3 items and upgrade them to 2/3, respectively. The Overflow already lists the 1/3 items. They could show everything listed above, too. Would rarely be used for Tier gear, but this is a deterministic way to target particularly weapons and cloaks.

To maybe save you some legwork identifying variants:

• [removed infos about the 1/3 variant, which can not be used to create LFR Tier]
• Upgrade 2/3 & Normal Tier: identify by bonusID 9343, to create use 9343:1507:8767
• Upgrade 3/3 & Heroic Tier: identify by bonusID 9344, to create use 9344:1517:8767

Update: sadly, upgrade level 1/3 can not be used to get LFR appearances after all. Edited out references to 1/3 & LFR appearances.

Sorry haven't typed out a full reply on this yet, but I do believe I have the proper tech in ATT to accommodate a system to handle the Upgrade aspect of items with minimal data maintenance required from what exists now.

As for Catalyst indicator, I am expecting more of a Tooltip-only situation to start with, but we shall see. But I don't expect to work on that until after the Upgrade tech is filled out.