More likely that we're heading back to the Milky Way?

Not necessarily.  I think Shepard and his crew's story is done (maybe not Liara and Wrex but writ large), I'd have preferred a new crew in the aftermath of the Reaper War.  Ideally BW would be able to resist the urge to bring back the old crew at every chance.

And lets not pretend Andromeda brought anything new.

So just a new crew in a completely trashed setting, which basically makes it a new setting?
And you still want all the old races to be there etc?

Struggling to see the difference from ME:A to be honest.

So? We'd still have them just under a different name.
Still can't see the difference here - ME:A is basically the continuation given how similar a lot of it is.

If you have a canon ending then every single person who played the game's choices are rendered irrelevant. You're looking at it as if you're the only person playing the game, i.e. "It's not like all my Shepards destroy each others stories"

For each ending I picked that particular Shepard's story is true. Since all are true, none are.

And since I'm not The Most Interesting Man In The World I doubt I have the cachet to say everyone else must bend the knee to my preferred ending...which, btw, is Refuse. They're all dead, Jim!

I think the point being made is that currently, any given player can make whatever decisions they wish across the trilogy, and end up with a final MW state that is essentially their personal chronicle of the Shepard saga. 

If they canonise one ending, then they've effectively labelled a percentage of the options as 'wrong' which will inevitably upset people.

FWIW I don't even think canonising an ending is that big a deal, my main issues with continuing in the MW boil down to the Reaper story essentially being the most important even in MW history - following on from that is either going to be a story of inferior importance or blatantly silly as a foe that could have challenged the Reapers suddenly arrives a few years after their 37 million year operation is stopped and it just so happens some plucky hero will arise just in time to stop them. Both options feel pretty unpalatable. 

At the very least, Andromeda has a lot more potential as a setting and the importance of the story in the OT has basically burned the MW as the setting for a new saga.

In his defence, he's not - I think the main thing grinding people's gears isn't so much that he's arguing his opinion matters more than anyone, but rather that he's not making any sense (his stance from what he's said so far seems to be words to the effect of 'I hate how Andromeda just rehashes everything so lets move the series back to MW so we can rehash everything and break the canon on the side')

I'd personally love a Mass Effect game that deals with galactic society in the aftermath of a Reaper War. Ancient forerunner civilizations and blasts from the past are gone, so we can look to the future. On the other hand, there's loose ends to tie up. How do the Krogan manage themselves in a post-Genophage existence? What would a united Quarian-Geth civilization look like? Who joins the new Citadel, and who doesn't? The Batarian Hegemony is completely destroyed but hundreds of millions if not billions of Batarians still live in Terminus space and need to build a new government. Pre-spaceflight species such as the Yahg are none the worse for wear following the war; what happens to them? What role does Shepard take, provided he/she survived the events of the series, and what role do the Reapers fill if they weren't destroyed? And what about the Leviathans? Are the former rulers of the galaxy content to hide on an isolated ocean world or do they view the chaos as a chance to rebuild their lost empire?

We get little hints of most of these (and other things) in the epilogue, but only to a certain degree. Of course, handling these in another game would require canonizing an ending, but I myself would not mind.

BG1 did have a canon ending, yes, because it presumed to had certain companions with you the whole time at the game's very beginning.  Without giving spoilers here, the better parallel would be the ending of BG2: Throne of Baal, which has options thematically similiar to the choices laid out at the end of ME:3. If they had come out with a Baldur's Gate 3 and imposed one of those choices as a canon ending, the effect would be similiar to what we're talking about with setting a fourth ME game in the Milky Way. When a player changes the ending from one playthrough to another, it's still their character and their choice. 

Wait a second. How come it wouldn't work for BG3 when it did work for BG2? You're not making clear what you believe the difference is.

Plus several characters can be encountered who could be dead in the first game.

And if "a lot worse" could work (and hey, BG2 is generally considered superior to BG1 in every way) then what's the problem with a canon outcome for Mass Effect?  Just make a canon that doesn't favor anyone's so no one can claim favoritism.