One key problem with Pretenders is this: take, say, Kingdom Core class Optimus Prime. The plastic blister bubble he comes in is essentially the shell. Asking for classic style Pretenders now is asking to take essentially that blister bubble (big enough to contain the Core class figure), but give it arms and legs and articulation and paint, and sell the entire package at retail. And even if that works out, you've still got a Core class figure that just doesn't interact as well with the rest of the line for most play needs. (And, of course, with all the parts-count and paint budget limitations of Core class.) Going smaller (Titan/Prime Masters) is even worse, and going bigger is even less of an option.
All for something that, as unluckiness points out, for most purposes (display in particular) doesn't even need the interior robot. Unless you're displaying the shell and inner robot side by side, which looks amazing but demonstrates precisely that one doesn't need to contain the other.
I think it could work as the successors to the Weaponizers. Make a robot that can reassemble into a vehicle or be disassembled into armor that is compatible with most figures but has extra functionality with their intended character. Release a deluxe Octopunch who turns into a crab and release deluxe Pretender™ Flotsam who turns into a boat and disassemble into gloves, boots chest armor and weapons that make Octopunch look like his shell. This also means you can put the diving bell helmet on other figures for lols.
Of course this isn't practical for every Pretender design.
This isn't a bad idea, sort of like the Beast Alliance armors or Cyberverse Spark Armor things. Bit difficult to juggle all those design needs though.
Alternatively, the shell could just be broken up into armor pieces and Centurions-attach onto the inner robot to give them the appearance of the shell. Rather than a budget albatross, the shell (armor set now) becomes a modular kit that can be marketed as mix-and-match with other Pretenders AND the rest of the 3mm/5mm peg-using line. They wouldn't need to integrate into the altmode at all, because the whole point is to armor up the robot mode. That's one less design requirement, and functionally not that different from most standard original Pretender shells anyway. (Pretender Vehicles could be more like Junkions, with the pieces armoring up and changing the vehicle mode from jet to car; Pretender Beasts could play with the inverse, making a regular wolf look like an armored wolf.)
I imagine this would still be a costly thing overall, especially if the inner robot was a Deluxe base to work with the rest of the line and have a decent budget for its own design. For instance, Deluxe Pretender Finback with fish monster armor pieces (boots, chestplate with ball-jointed helmet, back fin, arm blade, claw arm) would probably be a Voyager release.
