The only problem with putting it after ME3 is that they might be forced to pick a cannon version of events or have to have a lot of alternative situations relative to the different outcomes. Not only from the choice, but the effect the EMS score had.
Unless they set it far enough after ME3 so that any potential damage was/could have been fixed and therefore they only have to have a few different bits of dialogue. That at least means they reduce the number of major plot options they'd have to factor in, ie the outcome of the Quarian/Geth stuff. And even then that ignores the option you had to reject the obvious three end options.
(I would use spoiler code options to hide text, but I don't know what options this forum has for that, so I'm opting to be vague.)
Also the mako was fun, but blooming difficult to control, which didn't help encourage me to cover the entire map to see what wasn't already marked on there. Maybe some way of combining the scanners and the mako?
Hobby writer, here's my sci-fi;
https://www.royalroad.com/fiction/36579/endeavour