I've set the following bugs blocker for this action (please remove if not blocking... dur):
bug 18112 Retain URL as metadata on upload-by-url
This seems a critical bit of metadata for permanent recordkeeping.
bug 18200 Upload-by-URL has a different file size limit from HTTP POST uploads, needs to be shown in UI
This seems somewhat important to friendly UI.
bug 18201 Upload-by-URL should enforce $wgMaxUploadSize early when Content-Length header provided
bug 18243 Upload via URL: More meaningful error messages when HTTP error encountered
Seems common to get HTTP errors... more datas!
Actual feature loss, fixme please.
These are related but probably not blockers:
bug 18132 Support multiple file uploads with upload-by-URL
bug 18202 Upload-by-URL should run in background, report feedback interactively to user
Also, this one is related to bug 18200 and probably can be fixed at the same time:
bug 18411 The upload form only checks upload_max_filesize, not post_max_size