Creating a single market for telephony in the way you describe has never been the goal of these regulations. The basis for the discussion has always been that roaming was for travellers and customers would continue to get a mobile phone contract locally and operators have been fighting hard to keep it that way (see, e.g., this press release issued by the Commission last September).
The regulation should therefore merely make incidental use in another EU country easier. Concretely, I remember talks of limiting free roaming to a certain number of days in a given year and the Commission now seems intent on letting operators and national authorities determine what's incidental or not but nothing is final yet.
Importantly, roaming is free for customers but operators still have to pay to use another operator's network. This "wholesale" price is also capped, but (obviously) not planned to go all the way to 0. This means that in your scenario, the Romanian operator would have to pay quite a bit to the Swedish operator, possibly eating up all their profit. The restrictions I mentioned before are intended to allow them to terminate your contract if they can determine that roaming charges are disproportionately high and Romania is not the primary place of use (not that it will not necessarily be about any specific legal notion of "residence", the press releases uses the phrase "stable links" instead).
Unfortunately, this also means that getting a SIM card for long-term travel or keeping it alive from abroad could be more difficult than it is now, when operators can charge you for roaming and have fewer reasons to prevent customers from roaming a lot.