Meh, I find that to be silly reasoning, they fucked up big time with ME3's ending and they're too scared to do anything with it, let alone daring. Plus the new team understandably doesn't want to be saddled with that but all the same I find it be a weak move. Even then choosing a canon ending is something that wouldn't be a big deal in the first place, and could be mostly avoided with some creative writing.
Sure there would be a big outcry at first by a small number of people who don't understand how picking a canon ending to continue the series doesn't negate their choices, but who cares? Those people are self centered and small minded and will get mad about most anything. But it would fade relatively soon, especially once the game is released.
Secondly if they really want to appease fans and respect all the various endings and not ruffle anyone's feathers they could simply pull a Warp in the West and have all the endings happen. Pick the best of each ending and merge them into one. Geth live, EDI becomes organic/synthetic hybrid, Reapers die, Shepard is lost to the ether somewhere. Some shit like that.
Embracing the actual impact of such a monumental event like the Reaper War and possible destruction or disturbance of the Mass Relay System and then setting the game a few decades to close to a century into the future would allow them to gloss over many choices and outcomes already. They just don't have the balls to face and explore the disaster they created and outcomes that would result from it, which is a shame, cause it could have resulted in some really cool story telling and scenarios.