I'm hoping they have an end in sight on the Star Wars covers and don't feel pressured to perpetuate these variants.
I've really enjoyed them and have each one so far, but they'll certainly dilute the concept's novelty and fun as they start heading toward the more obscure characters. The first 9 characters released in '78 have already been done and I think that's your real core (Luke, Han, Leia, Chewie, Ben, Vader, 3PO, R2, Stormtrooper). Boba was essential and, with Lando added, I don't think you have many more main characters outside of Yoda. That's a nice set that collectors will want to display on their wall. Once you start going beyond them, you'll have less and less people that consider these "must-haves" for a set. I'm struggling to imagine anyone posting on here about how geeked they are to pick up the Lobot action figure variant. I can see doing some of the more valuable characters like Yak Face or even the Droids Boba Fett (in the cartoon color scheme would be really great) maybe as ratioed incentives, but we certainly don't need General Madine, Teebo or Dengar (unless there's a bounty hunters mini).
Gentle Giant has done the same thing with their 12-inch scale series and I think they have over 50 figures now. It just gets tiresome and I'm betting a number of the people collecting them still do it more out of the completist mentality than any actual enjoyment.