Providing data access when roaming isn't that expensive, especially with reciprocal agreements, so I fear we'll see surcharges to try and offset the loss of money that was made from pure greed and nowhere near representative of the actual costs.
If there was a small increase, which there won't be, I'd accept it for having a tariff that just works throughout the EU. Instead we'll get a rather cynical attempt to restore the money lost (or to be lost) through this amazing cash cow.
And let's obviously remember that we're only talking about the EU. Go beyond the EU, or even to places like Switzerland or Turkey, and you'll still get shafted big time. Possibly more.
In theory competition would solve this, and we'd also see networks expanding schemes like Feel at Home, but it's clear the industry is still being quite protective and not going too far.