From this news, it seems like any supposed stand alone price would be 19.99, which i think would be absolutely fair, but if they won't bite, i can't really see why i would to buy IW.
Leaving money on the table
Pretty obvious from this thread that if it was separate, everyone would just buy and play that instead because they're not interested in what Infinite is selling. Me included.
Like I said, it's a good business decision to hold it hostage for awhile as incentive to sell $80 worth of product.