MinionZero, im not sure if your agreeing with me or not.
I suspect we're looking at the history of seatbelts from a slightly different point of view. The use of seatbelts was brought in gradually, and when it became clear that they were an excellent way to save lives it became law that they be installed on all new cars. However, it was not originally required to retrofit them into old cars, because it was identifed that doing so would lead to backyard jobs that could actually make things more dangerous (fix the seatbelt to the wrong spot and you could, for example, reduce the strength of the bodywork so that in an accident the car buckled worse causing more damage). It was only about 15 years after the original law was brought in that the requirement to retrofit was introduced. And by that stage, there werent that many cars left to be retrofitted and the installation of seatbelts was a well known task, so retrofitting could be done safely and without risk.
That would be the way i see the introduction on parachutes being brought in as well.
I suppose for me the current situation more closely resembles the introduction of airbags into vehicles. Its not a legal requirement to have an airbag in your car nor the types of airbags to be used (driver, passnger, side, etc). However, you would be hard pressed to find a new car being sold without airbags, and if one did exist it would have to have some other amazing selling points to have people buy it without the added safety feature of an airbag. Additionally, i think you would be very hard pressed to find anyone who would try and retrofit an airbag to an old car, the cost would be high and you would have no guarantee that it would actually work as designed because the car was never designed to have the airbag in the first place.
So im all for parachute technology being brought in for new aircraft but i think its an incredibly risky proposition to have old aircraft retrofitted...