I'd pay for previous expansions' collector items. I missed a decade of expansions and I'd definitely like to get the items.
Edit, I think I mis-interpreted this. Meant collector set items, not collection items. . . . They do offer the collectors set for sale once in a while, though I would be more apt to buy things if they were for sale individually. Nothing to see here. Move along.
The last part would be the sticking point. They are Slowly doing this now. I think that the plan is to eventually have it on a rotating schedule similar to what the LoN Loot card packs are.