What a fabulous looking quilt. I don't think SID would be a big deal at all if you zigzag every horizontal row, turn the quilt and then do it again the other way. It would mean sewing one block side, stopping and turning the quilt a bit and then doing the next block side, i.e., zigzag. Even if you did just a few rows each day, before you know it, you'd be finished.
I did a king sized quilt that has 222 large "melons" in it. I stitched in the ditch one row at a time, having to stop at the end of each melon and turn the quilt the quilt slightly to do the next melon. It didn't take very long and, just doing a few rows at a time, it was not an overwhelming chore. If you consider that each melon has 2 sides to SID, except for the very outside rows, that's stitching along 404 melon sides.