It would be a nice idea to bring back players, but for the wrong reasons. Some would come because the servers would be fuller, but a lot just for the xp.
I for one prefer smaller battlefields, and this would make me play much less on Sundays.
And strat battles should imo not be affected, since otherwise they would be mostly condensed around that day.
Also, iirc this has been suggested every single time a double xp event happened, and it has never happened. Part of the reason could be that they are rare, and thus treasured, and making them regular would take away a lot from them imo.
I would not like it, a lot of the playerbase would, but I doubt it would ever happen.