Suggestion 1, Instead of "Legendary" eqps, reintroduce "Ancient" eqps, not 100% sure if they were removed or not but i have no seen one in what feels like years. They had a nice stat buff that wasn't too over the top.
Suggestion 2, Perm. "Event", as you said no cash shop. So if you were introduce a "Goodies Bag" which could contain anywhere from creature res, feather, SS to possibly e-pro. It would more then likely contain a mere 1 of each per bag drop but would be something to keep those hard grinders like myself happy.
Suggestion 3, included in the above bag, a VERY minimal chance at an "Ancient Element Box" Which would contain from a rank 2-7 (in slightly decreasing odds) strike or defense element or possibly even a skill element just to add another variable to it. This is both increasing the access to enchanting gear while i believe keeping it at a steady enough rate.
Suggestion 4, working with thndr's suggestion. Instead of introducing "soul pet card" add a tamable value to existing non soul pet empty cards.
For example: Loot Empty Blue Pixie, Find a " 'Blue Pixie' variation" (Cant think of a suitable mob), Tame said variation and result in Having a "Blue Pixie" with identical stats, skill tree but with an altered Picture and model.
This would keep a market for the default pet cards while still allowing for demand.
+1 for staging, but with no advanced cs staging material (adds to risk of staging but gambling can sometimes reap rewards), but keeping joker (Would add for a sweet pet if nothing else )
Not sure if these would be possible and if so how difficult. But i will keep upto date with this topic and lend my opinion if needed.
I feel like if they were to do a Runescape and release an "Old School" server with the same poll system, it would increase revenue for them insanely. But until then, we will have to fix their stupid mistakes