Contact import progress - multiple issues

1. on Wordpress, the contact import progress bar does not work. The GET status requests are made, but the server does not respond to them until the import is complete. What's worse, multiple requests for import keep piling onto each other, bloating up the web server, eating up PHP processes. See Chrome devtools photo. File used for import is attached - it's just an export of all 160 sample individual contacts in the demo site.

2. on Drupal, the contact import progress works, but jQuery raises the following warning: "Synchronous xmlhttprequest on the main thread is deprecated because of its detrimental effects on the end user's experience." Perhaps this is worth looking into before the functionality stops working in future jQuery versions

3. the existing progress bar implementation is a great opportunity to move to a batch-based import processing implementation. I see that although progress is updated periodically, the work is still done through a single, long POST request. Batching would eliminate problems with max_execution_time limits, out of memory errors, and so on. Is this something that we might see in the future?