Is a somewhat related question "how long are the various commercial
support organizations committed to supporting 7.4"?
I guess support companies might support their client's systems
for longer or shorter times than the community patches the old
versions. No doubt it's easier for them if the community
does the backpatching. But if any of those companies has
a lot of 7.4 clients, they might be tempted to deal with
backpatches for their clients even after the community stops.