No. Nobody has written a plugin. Probably because contrary to flickr, Facebook, smugmug, etc. Apple hasn't documented publicly how to publish to iCloud.
iCloud is a storage system not a Photo viewing/publishing system like photo publishing sites listed in the above reply. I can't go to iCloud and View the images you have uploaded to it. IO would need to Log On to your account to be able to see those files. Even then they would look like any other files you have STORED on iCloud.
I guess the idea (which I would also like) would be to "push" pics (once they have been developed in LR) into iCloud Photo Sharing service and easily share this way with e.g. other family members (my wife hates using 3rd party apps like SmugMug etc.)