I don't know, look at Star Wars. The Skywalker line is a on going legacy and the fans love that stuff. I really don't see why we need to abandon the Shepard name entirely, not like any other game had such a character that it caused confusion with ME. So Shepard's cousin joined the Ark program, maybe after all Shepards done the Alliance wanted one member of that clan to join the survivors. Maybe after a generation or two in space, one of those surviving Shephards decides to join what's left of this Alliance thing and becomes the next hero in ME ie Andromeda.
There you have it, keep the Shepard name, people are attached, yet it's an all new protagonist for a new direction in the series. Some expert writers can fill in the gaps that I haven't and were done, the Shepard is Jesus parable continues.