Implementation of load balance algorithlms

Hi, I find it very convenient to use load balance interface like in moderngpu:
[https://github.com/moderngpu/moderngpu/wiki/Load-balancing-search](url).
Many of the problems I encounter is given many segments of workload, while each segment has different and irregular granularity of workload, which makes the parallelizing difficult.
With 'transform_lbs' provided by moderngpu, I can pass in a lambda function with the arguments
(int index, int seg, int rank), where index is global position, seg is the segment id, and rank is the offset inside the segment.
I wonder why thrust does not provide this kind of interface. Or Thrust can actually support it, but need to implement it with several API calls.