No,
I think Mass Effect would have been shelved either way and no DLC was planned. Just get the game out and move on to Anthem.
Bioware's most successful game was inquisition yet the next game has minimal people working on it as they are all working on Anthem.
I also think people were overly critical of the game after the ending of ME3. Is it an amazing game? No it's a good game with a few design flaws but I was happy with it.
There were a bunch of side-story cliffhangers that were pretty clearly meant to be resolved in DLC so I find it hard to believe none was planned