It’s actually more expensive especially when the transit providers are in conflict with each other (I believe the money is a root cause), so you need to serve some proxy servers to convert IPv6 to IPv4 and vice versa. These servers will inevitable will be a point of failure and the bottleneck for the high amount of traffic. The alternative is to disable the IPv6 routing on those segments.
Too much troubles for nothing.
When we have had a Community Satellite Stefan, the rule was: