Apple will most certainly stop this from happening. Possibly by requiring all 4S phones to be updated in order for Siri to work, and them locking out non 4S phones from accessing the service.
Honestly, this project is nothing to get your hopes up with.
I was initially very excited, but after doing the slightest bit of reading into it, I have to agree. From the FAQ:
...we have to intercept the data that is being exchanged between devices to initially trick Apples servers into thinking that the device is authorized...
The way I read this, they are essentially creating a program to hack Apple's servers. This being the same Apple that has teams of IT, server, and security experts along with the lawyers to back them up!