I don't think we need a new installment in the EarthBound storyline, given the fact that Shigesato Itoi wanted to end the series with the third game and wrote it specifically to be the grand finale; unless Itoi himself decides to make another follow-up, it'd feel wrong to mess with that artistic vision.

I would, however, be open to the idea of remaking EarthBound Beginnings in the style of Mother 3, considering that the former aged about as well as a bucket of unpasteurized milk on a summer day. I'd also be fine with a Mother 3-style EarthBound remake, though I wouldn't consider it as necessary.