Idk how the devices work but if you have to replace them to get the extra capacity, it would still cost the airlines money, and the FAA has historically been very friendly with airlines.
It's not about cost or technology. The pilot's union is against longer recordings.
And cost, according to a FAA quote in the linked article.
Retrofit would cost money. But mandating years ago that new planes and anything going throw certain levels of maintenance would have update would not be that expensive.