I think this is a flawed notion, I chose BroShep for one run through and FemShep for another. What drew me in was the overall story and my interactions with the crew.
Real fans of the series would probably enjoy whatever route they took as long as the story was cohesive, made narrative sense, and they nailed the crew.
You could easily bring back the VAs for Garrus, Wrex, Tali, etc to voice the characters and that would go a long way to appease the fans.
Also, Mass Effect is a big franchise but let's not act like it's a massive fan base, at the end of the day, a good show will be good and that will draw fans, many who will probably have never played the games, in.