I will start with the fact that good tamper proof package may come with additional costs people may not want to pay for.

Let's say that there's an issue with package's content and the sender claims he sent everything right, the recipient claims the content is missing/incomplete.
Do you have a good way to find out if it's the sender or recipient lying or any of the "couriers" was skilled enough to steal without leaving traces on the package seals? How will the reimbursement handled?

Also, how about bitcoin price fluctuations? Will the "couriers" be able to "speculate on the price" because of the collateral they pay?
Still on collateral: the couriers will know when a package is expensive, making it a good target for stealing/tampering.

Then the income: how you split the shipping price between the couriers? Time and distance are not enough as factors (rush hour, or remote areas are probably more important to take into account).

Imho unless you have experience already of a shipping company,... this is going to be difficult to make it run well. Good luck though.