In some form yes, but I am assuming a few things,

1. There is a Queue which utilizes multiple connections, this works and the code is there.
   
2. A sync job produces a change list (up or/and download)
   
3. Pass this list (2) to (1) (push to background)
   This should result in using multiple streams (connections) when processing a change list.
   
   It would be nice if #4 can be done, but I can use autoit to control the GUI steps in an automated fashion.
   
   If #4 is really complex, let's discuss #4 at a later stage.
   
4. Introduce a script switch which does the same from a script job.
   

Thanks. Though to avoid disappointment, after seeing your other post:
How to speed up file Synchronization using SCRIPT? Any option to enable multi-thread or multi-files?
... this tracker request is about GUI. It has nothing to do with .NET assembly or scripting. That's completely unrelated and completely different level of complexity.

I've send you an email about donation and maybe to sponsor this request. Pse. have a look at my email and indicate what the minimum requirement is for sponsorship.

Thanks for your suggestion.

I have added this request to the tracker:
Issue 2318 – Optionally push synchronization actions to queue
You can vote for it there.

Allow lists such as from synchronization results (preview changes) to be pushed to the queue (allow use of multiple connections).

I am aware synchronization from a script using multiple streams (connections) only works from C# and PowerShell (which are complex scripts compared to the default script from WinSCP).

But when you upload/download multiple files in the background (Queue) it uses multiple streams just fine, so why not push the result list from a synchronization session to the Queue and benefit from multiple streams? (and of course have it available from default WinSCP scripting).