ACCC conductor is a significant upgrade and has tremendous advantages. There are many applications spread across North America where replacement of existing conductor with this would be very beneficial. However, as I have cautioned before, increasing the thermal capability of a transmission line may negatively impact reliability.  If the system has a stability or voltage constraint, there's no guarantee that carrying more current across long transmission lines will not exacerbate those problems. Detailed studies need to be conducted to ensure that the system responds reliably to the prescribed NERC contingencies with the higher current carrying capacity. Also, just because the upgraded conductor can carry two times the current that the old conductor carried, that doesn't mean you can just slap it up in place. Engineering would need to evaluate all the associated gear with the transmission line, insulators, breakers, transformers, busbar segments, wave traps, protection systems, etc. Some of those components may also need to be upgraded which will up the cost of the overall project. All in all, it's a good investment as long as it works reliably and doesn't break the bank.