Great minds think alike. I also agree with new wide/narrow chainring (so must be EVEN number of teeth) in middle position on the current crank, as hollowtech 2 and external BB bearings are a great setup. Plus, the middle ring on a 3X should be right at the target chainline dimension, if your new cassette has the same overall width as the previous one. Only if you wanted a really small chainring, which would need to mount on the inner position, would the chainline be off.