Description of problem:
It would be useful if there is a way to upload the ruby gem to copr, if the ruby gem is unpublished or if you want to build the latest gem instead of the one in the ruby gems.org website or if the gem is in the pre-release version.
That is too broad. Even in your #0 is too many "or". If you want to create rpm from *some* gem. Then I recommend to use "gem2rpm --srpm" and submit resulting SRPM.
If you submit patch I may consider it. But otherwise there will be no time to implement this. So it is rather fair to close it. Sorry.