I want to belive that AMD is no forced to populate all 8 chips on the big I/O die.
However, it doest make some sense to assume that they might want to use at least 4 chiplets (functional or not) on each ThreadRipper part for the same reasons as before. Perhaps it's less necessary now that there's a huge IO die in the middle of the chip to balance the IHS on, but it still seems reasonable to assume they will.
Whether they do or not should probably give us a good indication of what their yields are like. Since they moved most of the IO off of the chiplet, there isn't going to be anywhere near as much die area where a defect outright kills the chip.