I think all three of your proposed versions (A,B & C) should be supported. They all make sense.

Also, don't forget that http uploads would need the exact same abilities (including sending multiple files to the same URL, such as http://some.site/posting.acceptor.php).

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Here's a thought I had, for what it's worth. It doesn't add anything to your proposal, but it might serve to further spark the brainstorming...
It seems to me that this problem is very similar to the existing ability to specify alternative output filenames for downloaded files (except, obviously, in reverse).
I believe you currently allow the following:
1. curl -O http://some.url/some.file http://some.url/some.other.file
  -> Uses the remote site's filename in the Current-Working-Directory (CWD).
2. curl -o file1 http://some.url/some.file -o file2 http://some.url/some.other.file
  -> Uses my filenames (file1, file2)
3. curl -O http://some.url/some{1,2,3}.files
  -> Uses a RegEx within the remote URL (I don't know if the syntax is exactly
     right, and I don't know whether a similar regex is supported for -o filenames)
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Thanks,
- Kevin
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