As with https, moving forward has a cost, but at some point, the cost of staying compatible with old protocols is higher. Before the switch, you have to deal with training staff for the new tech. Once the switch starts happening, you need to train the staff to deal with the risks of keeping the old tech.
For example, I find it easier to have an https-only web infrastructure. Too bad for old deprecated browsers who cannot support proper encryption (and therefore become a security risk for me, and a waste of time to support). Dual protocols (v4 and v6) take more time and money to manage. Initial training can be harsh. Some first-gen hardware was terrible. However, now that it's done, I can't wait to switch off IPv4.
For example, I find it easier to have an https-only web infrastructure. Too bad for old deprecated browsers who cannot support proper encryption (and therefore become a security risk for me, and a waste of time to support). Dual protocols (v4 and v6) take more time and money to manage. Initial training can be harsh. Some first-gen hardware was terrible. However, now that it's done, I can't wait to switch off IPv4.