Been a while, just wanted to update status.
We ended up developing the desired functionality in the client's Alfresco API wrapper, where all operations from different projects join together.
Just before the upload methods. the desired folder structure is created, and documents are directly uploaded to their destination.
Via opencmis library, no concurrency / thread-safe issues
However, solution is not generic enough so as to benefit from it
@iblanco thanks for the insight, seems we're all working on the same direction, stepping same rocks in the way. guess we require a more advanced knowledge / time, in order to provide a solution, compatible with current architecture design.
@tfrith, thanks for the idea, but one of our requirements is to make all the upload operation, up to the destination folder, synchronously, so no option for batch movements afterwards.