What is with all the people and the legality? In case you haven't noticed, you're on a forum all about emulators for Warcraft...
If you want to make your own server and have it successful, you need your own niche that puts you above the rest and heavy advertising (Advertising is easy though). These days, that's not too easy, the niche that is. I would stay away from paid features however, they can put you in Blizzard's radar unless you're hosting internationally in a country that does not recognize Copyright law. The downside of that is limited demographics though. Statistically, international countries (England) have faster internet connections than the US, they can manage to play on a US server with minimal latency but people in the US have a hard time playing on international servers.
You can look at recent servers that ARE successful. Just off the top of my head, ScriptCraft. Started in I think early 2011. Their niche was an extraordinarily well coded Blizz-like Vanilla server and they advertised constantly before they opened their servers. Opening day, within an hour there were tons of people playing. So it is possible but difficult.
You will never have a popular server using an open-source core though.