rpm2module fails with just ‘No package found in repo’ when one of the packages given on the commandline can’t be found. It should list which packages are not available to make debugging easier.
It also isn't obvious from the help output that only names of binary rpms are valid input here, one could also want to have everything that a certain srpm builds in a the new module like
./modtools rpm2module vim
This will currently fail as there is no binary vim rpm, only vim-minimal, vim-enhanced, vim-common and vim-X11.