I also worry about how deep his romance will be if he's such an exclusive one. Only a small percentage of players are going to roll elves, after all.
According to DAO telemetry, Zevran was the least popular of the four romances. And I will fight anyone who tells me his romance was even one inch less deep than the others - it was actually the deepest, best written, most well developed romance of them, in my humble personal opinion.
So I wouldn't worry about the depth of his romance based on a presumed number of players who will experience it. I'm positive it has been written with the same depth and care as any other romance in the game.