The designer ? He does not have to touch any chip, it can be open-sourced, and taken from good a fpga design.
Obviously this can't be open-sourced due to its very nature, because if we pooled together $300,000 for a group buy, most of it will go into the IP. Someone who didn't participate in the group buy can just run to the fab with the open source design and spend his $300,000 entirely on the hardware.
The foundry can already do this, I doubt foundries would be running with the money. They usually do what they're paid to do, it's not of their concern what the chip does, except checking for IPs.
If AMD's fab, TSMC, started selling a CPU that perform exactly like Bulldozers, everyone would notice immediately.
If this group buy goes through and the global hash rate sky rockets, no one will suspect that TSMC is behind the scenes pumping out more chips than what we ordered. Even if such suspicions do arise, nothing can be proven due to the anonymous nature of mining. So TSMC has nothing to lose and everything to gain.
Packager ? They could be required to give back every bad chip they get.
That would work if you're willing to patrol the floor and audit every shift. Packagers have no incentives to steal now because selling the stolen goods would be very difficult like I mentioned above. However mining chips are different because they don't need to be sold. They can used to generate profit legally and anonymously.