Is it possible to validate whether all assets in an entry have been uploaded?
I do not believe there is an easy way to do this with Craft out of the box. Uploading 2k images to an entry is a bit of an edge case. I would recommend uploading all of those images directly to the asset volume. 

That being said, you might want to search the plugin store to see if anyone has created a plugin like this. You could also create your own plugin, copy the code for the asset field, and extend to notify when the upload is complete.

Good luck!