The company that publishes that game takes advantage of those numbers every day.
So does Blizzard with World of Warcraft. My point is, the majority of the people who are playing those games are not a ready-made set of people who would just pop over into an open-world giant arena PvP game. There's a big difference between people who will play round after round of WT for 20 minutes at a time and people who want to look at a map and figure out what to do for their play session.
What do you consider "polish"? Graphics? I think the current graphics are actually quite nice give the scale they have to support.
I personally don't think the graphics are a huge issue, but I do believe for the majority playing those other games, they don't care about the scale, all they see is "Other thing shiny. This thing less shiny."
To me, new guy experience and ease of configuration are the elephant in the room. A really excellent in game run through to get your basic controls, communication, and views set up I think is probably the biggest thing they could do to help get people into the game. Mouse controls would be high on the list as well I guess although frankly I don't see how you make mouse and keyboard equal to a full HOTAS/pedals/VR setup.
Personally I wouldn't even bother trying to get/keep the people that want to have 5 fights in 10 minutes after upping. Making the game something like that isn't going to happen without completely restructuring the game. Maybe more varied town/field layouts to work with would be a plus.
Beyond that, more vehicles. Fill out the planeset with more stuff that can be used in FSO and scenarios.
Wiley.