I think this will gradually bring player prices back in line with what they were before the Neymar sale, after which they exploded. Very few clubs could afford £60/70/80 million transfer fees before the new rules and even fewer will now. So the fees will come down.
The other thing that will come down is wages, as they also count towards FFP. This will likely be more gradual than transfer fees, but we will likely see most high earners close to £200K rather than £250-300K.
Put these two together and the result may be less player movement overall, which may or may not be a good thing. It will also force clubs to develop players more than they do now. I can see a lot of the action being in who will snap up the next 15/16/17-year old talent more than it is now.
Of course I could be completely wrong, but will be interesting to see how all this plays out.