Are talking two different but important things.
1) The SKREEM module
2) Replacement Key Fobs

The second is actually the easier piece with one exception, the RFID chip
Physical key - can be cut by any locksmith
Shell (with key) available on eBay
RKE circuit board - can be programmed in car
RFID chip - I suspect this is actually easy to copy with stuff from eBay or Amazon but I do not know how as yet.

The first, the SKREEM module I suspect is going to be more difficult to create one that "loses its mind" and just ignores the RFID chip.

Can be done, just needs someone to do it.