That's exactly what BioWare has been saying since Mass Effect 3 was officially announced. ME3 was always the end of Shepard's story. They've never given any "wiggle room" that Shepard would be in future games.
TBF BW said a lot before ME3 was released, some of which has come true, some not.
By itself I'm fine with Shepard's story ending, if it's a satisfying end. ME3's end didn't work for me at all. It does for many people, and good luck to them, but personally, I don't really want to invest in something else that may well take 5 years and hundreds of hours of play, only to deliver me ultimate disappointment. Again.
The only other thing that's been confirmed so far about the next game is that you WILL play a soldier again. No word of prequal, side-qual or sequal, and probably won't be for some time to come. Their teams are still 'reviewing the feedback' from fans.