I'd just mentioned the I41/I43 paradox in another thread taking about opposite direction interstates a few weeks ago. I personally think the I643 would have made the most sense, especially since as it stands now, everything South of the zoo interchange (I94/I894) on I41 is duplexed just so they can claim it reaches the Illinois border (and I894 is now essentially a pointless designation), but I41 does fit reasonably well otherwise, since it does generally lie between I39 and I43, and the overlap with US 41 actually reduces some confusion since most of the affected section had already been freeway for years.
As far as I11 goes, making that an extension of I19 would seemed to have made more sense, especially since there are hopes that it will go to Nogales anyway, although, I've never been able to figure out why I17 and I19 don't share a number already (or get numbered as Spurs of I10), since
they are both short Spurs that don't really leave Arizona.
Although I winner if they had made I11 a continuation of I19, would they have kept up the metric numbering?