Eurogamer's interview with Mac Walters, who was a writer on all three games in the Mass Effect trilogy before becoming creative director of Mass Effect: Andromeda and then Mass Effect Legendary Edition's project director, makes for a good read. Going all the way back to the series' origin as "Jack Bauer in space", it's a revealing history of BioWare's work on Mass Effect.
Some of the most interesting material covers Andromeda, which Walters joined late. He'd been working on Anthem along with most of BioWare Edmonton while Andromeda was being developed by BioWare Montreal, previously a support studio responsible for most of Mass Effect 2's N7 missions, Mass Effect 3's multiplayer, the Omega DLC, and so on. Only after Mass Effect director Casey Hudson left BioWare in 2014 was Walters moved over to work on Andromeda, so his answers mostly focus on the later stages of its development.
However, he does confirm the claim from a report on Andromeda's troubled development that it was originally planned to have a procedurally generated galaxy, inspired by No Man's Sky. "Ultimately, that was too much at odds with a lot of the way that we tell stories," Walters said, "and the way that we create our content, which tends to be very bespoke—a lot of big set-pieces and things like that. It's hard to translate into a procedural world."
When Walters was brought on, Andromeda was "in that pivot point, in that sort of inflection of, 'Oh we can't do both procedural—all of this stuff—and fulfil all the wishes and hopes of our fanbase who really want to see a lot of this bespoke narrative written in a certain way." Another challenge was that "there were just a lot of things that we had to relearn, re-figure out", presumably due to the switch from Unreal to the Frostbite engine.
Walters suggested that, to avoid some of Andromeda's problems, "we probably should have—in hindsight—just reduced scope more and executed on what we could to [ensure] quality. But, we were also in a weird phase in the industry where a lot of people were saying quantity was quality, so we were deluding ourselves internally a little bit that if it's maybe not as polished as [Mass Effect 3], it's fine—it's bigger and there's more here, and there's more to do."
This was during the period where, as ex-BioWare developer Manveer Heir said, Electronic Arts was "pushing for more open-world games" because they were easier to monetize. Other publishers felt the same way, and the result was an era of bloated games with maps full of repetitive blah. Plenty of Mass Effect players, fresh off a trilogy that grew more reactive and personal with each entry, were unimpressed that Andromeda was one of them. Walters called it "a lesson learned", and said it's a shame the studio didn't get a chance to show what it learned with a sequel. "I only wish we had been able to then do a second one," he said, "because then you would have really seen that polish just like we did from [Mass Effect] to [Mass Effect 2] on the original."
Instead, after Andromeda's release BioWare Montreal was demoted back to a support studio role, and then merged with EA Motive. Which is why the next Mass Effect will be made by BioWare Edmonton, and it looks like it'll be made using the Unreal engine. It's apparently still in pre-production at the moment, however, while the studio focuses on Dragon Age: Dreadwolf.