Ugh absolutely not. First of all the first contact war was more of an incident than a real war. Second of all I don't want to play a game that does nothing but rehash history. Let's move forward not backwards.
You can have games set in the past without them rehashing history in the same way there are endless games set during World War II. It's a matter of changing scope from "does the universe survive?" to "does this crew survive?"
There's lots of room in the universe for stories, as seen by ME Infiltrator and the other iOS games and the assorted novels. And stories of heroes doing this during the Reaper war would be interesting.
Such as the story of mercenaries going from guns for hire to something else as the war progresses. Or criminals making a living in the background of the larger galactic conflict.
I'm in the camp that compares this to the Star Wars EU. Going forward in a meaningful way means making a new threat. Which gets into Yuuzhan Vong territory. The big tacked on threat that comes out of nowhere because the signature conflict has been removed.
I just don't think a game set post-ME3 will be easy without having two skins for every character to reflect synthesis or non-synthesis endings. Let alone having to potentially deal with all the other changes. The amount of different dialogue options is staggering. And with the different game systems at play again, they'd have to set-up something akin to a Mass Effect Keep.
The fact is, everyone would want them to visit the key places in the ME universe, to see the outcome of their choices at work. (The absence of which was a big complaint with the ending of ME3), but some of the choices are too contradictory to be viable. Tuchanka would look radically different, as would Quarrian settlements. So the game would have to steer clear of those places, which sets people up for disappointment.
"Here's the new Mass Effect game. Return to one of your favourite sci fi universes! Now set exclusively in the Drell and Volus territories!"
So many people in thread have railed on ME3 being "rushed out" despite having a longer development cycle to the first two and being released a year after it was expected to launch. And part of that feeling was likely because ME3 is pretty much two games. So many choices carry over than things that quarter of the spoken dialogue probably didn't apply to a single playthrough.