Oh, sure, there's ways to require multiple keys. I would be surprised, though, if they seriously considered a plan that involved more than 2 keys (two keys is approximately equivalent to getting a warrant - keyholder 1 wants to do it and keyholder 2 says okay).
However, at a purely technical level, there's going to be something that does the decryption, and it takes the keys. There is no way to guarantee that it cannot be hacked to either work without the keys or leak the keys when they're used, and if either of those happen, eventually you have folks using the decrypter who shouldn't be.
There's also the fact that there's no technical way for this plan to prevent corruption/collusion amongst keyholders. More keys requires a bigger conspiracy or more social engineering, but enough keys to make that really infeasible also makes the decryption itself unwieldy, at which point it'll get bypassed somehow (shared keys, decrypting bigger chunks to avoid having to do more individual operations, etc).