When HP and USAir merged, circa 2005, US adopted SHARES. I was a heavy USair traveller at the time, but remember the constant frustrations of both pax and airline staff caused by the unfamiliar command structure required by SHARES. Mrs. NY-FLA continues to use USAir, and one of her itins consistently uses a NY-DCA-FL routing that uses the same equipment on both legs. Upgrades on both segments? Simply impossible to accomplish by any of elite line, airport check-in agent, or GA.
Haven't personally experienced the CO-SHARES random seat swap yet, (DL pricing is keeping me over there since << 3-3) and don't remember seat swaps as part of my US-SHARES experience, but with CO's cavalier attitude to forcing seat swaps to achieve higher order social engineering goals, and SHARES general intransigence in all but the most skilled hands, this sad state of affairs seems predictable.