Here's exactly what they said:
Flynn mentioned that it’s long been a regret of Walters that they spread the Mass Effect story far out over the entire Milky Way galaxy, with the game’s galactic map showing a civilization that appears to stretch from arm to arm without too many unexplored nooks and crannies.
"With Andromeda," said Walters, "our goal is to start that at a much smaller scale—though the scales are still massive—and give you a sense that there is much more to explore, rather than saying ‘here’s the whole galaxy.’"
I fail to see the logic here. They complain of Milkyway being too small yet now they claim on starting small in Andromeda and expanding it. Why not expand the Milkyway instead? oh wait... Starbrat
they can just add more stuff in the Milkyway you know? those "arms" of small civilization were the result of mass relays. In 2006 the focus was giving a game with a great story! and it would be technologically difficult or near impossible to create an open world sandbox game at that time. Even the first crysis was pushing computers to the limit in that year.
But if BIOWARE IS SINCERE they can keep the original design of the Milkyway and update it. That is no longer possible now due to ME3 which basically crapped on everything so the proposal of OP is believable and prima facie evidence that Bioware wrote themselves into a corner.
The reasoning of Bioware that the Milkyway is way too small so that they have a feeling to ditch it is also illogical. You have to start small somewhere and improve on it, Crysis proved this. There were many games before it with open world aspects like the Elder Scroll series but it was no where near the cryengine simulating reality and sucking the player into the world.
Mass Effect 1 had these goals, that's why the open world barren planets are there including the Mako in order to give the players the illusion of being a total explorer or astronaut. This only weakens their position on ditching the Milkyway where their goals began because they have the ability to fix it and improve the Milkyway but was stopped in their tracks due to ME3. Andromeda now is the "Alamo" of Bioware for the Mass Effect franchise in order to save that goal or dreams of exploring a big Galaxy, that feeling of being an Astronaut... sad to say the place where that dream originally began is now deleted. Bioware is trying to redeem itself a second chance shall I say.