The two are tightly related, although physical movement is more important because in absence of it you waist a lot of time to get a Visa and there's always the possibility that you might not get it, whereas with roaming charges it's only a matter of convenience and price.

Btw, whenever I travel within EU one of the first things I do after landing would be to get a PrePay card. In European countries PrePay offers are really good and sometimes better than PostPay contracts.

If anything, I fear that this will favour an oligopoly of the big ones, like Vodafone and Orange, with no real benefit to me, a user accustomed with searching for good local PrePay offers.