Does it really make that much of a difference? Having consistent flight numbers like you suggest would be nice, but they've just made it consistent in a different way (sCO vs. sUA). Besides, while accelerated since the merger, many of the flight numbering schemes for domestic/Canada flights have been made inconsistent going back well before the merger.

Besides, on my list of things I care about when flying or choosing an airline, flight numbering scheme ranks pretty close to, if not right at, the bottom, and I'm sure for many, ranks below the bottom.