If the game is a hit I can see the Orks being the main force followed by the Space Marines, then Chaos Space Marines and finally Eldar. I'm really hoping the F2P aspect of it really makes the Orks the main threat for every faction, just like in the lore
Of course, with F2P, orks will be the most populous faction. Only factoring players that bought the whole game, or a seperate race if they start from F2P, I would guess that Space Marines would easily take first place. I think orks (paying orks that is) and eldar would compete for last.
I'm not too sure yet, although I would say Orkz since that's the reason why they're going to be free to play but then again you have to have people who are willing to play as orkz. So far, I've not seen many players dedicated to orkz...
What I don't get is how do they plan to have people play Eldar/SM-CSM at launch. I mean, will beta player have access to all races during Beta? Will there be a trial where we can try a race?
As I understand it, you'll be able to make a character on each faction. But they have not explained how they will combat people from logging out and switching factions based on who is winning.
They haven't explained much of the coming beta, however I imagine more details will be revealed in due time.