how to create index concurrently on paritioned table

Hi hackers,

Partitioning is necessary for very large tables.
 However, I found that postgresql does not support create index concurrently on partitioned tables.
The document show that we need to create an index on each partition individually and then finally create the partitioned index non-concurrently. 
This is undoubtedly a complex operation for DBA, especially when there are many partitions. 

Therefore, I wonder why pg does not support concurrent index creation on partitioned tables? 
What are the difficulties of this function? 
If I want to implement it, what should I pay attention?

Sincerely look forward to your reply. 

Regards & Thanks Adger