Yes, cloud support is planned. With the cloud drives you mentioned, sidecar files sounds like the easiest way to ensure tags and ratings are synced between your Android device and the cloud. Flickr has tag functionality in its API so you can keep them in the image. Initially, cloud services will most likely be view only with basic functions. We will build out more popular cloud services first.
As for the tag length, this will be improved with the new tagging system I mentioned before.
