This wouldn't really work for AMD processors... They could design and fab a 6-core chiplet, but it would need to be the same size as the 8-core chiplets so it would interface to the same carriers. If the footprint is the same, the fab cost is roughly the same, so spending the design time on that doesn't make sense. If they build separate carriers, that's more design time and inventory management and it may well be more expensive than just building 8-cores and disabling two.

That said, with Zen6 having 12 cores per chiplet, I wouldn't be surprised if they eventually end up designing a smaller chiplet with 6 cores and a dedicated small chiplet carrier. Or push 6 core SKUs to the APU side that doesn't use chiplets, Zen5 APUs already have specialized masks for some of their SKUs.