Not a new idea. This was submitted as an idea over four years ago. It is still a problem for many users.
Please expand s.purchaseID to support unique strings larger than 20 characters. 64 characters would be just peachy as it would support a SHA256 output.
While we're at it, it would also make sense to expand the values that you can add to custom events (for serialization) to the same 64 characters as opposed to the existing 20 characters there.
Adobe, let's get this done.