I can't think of any good reason to keep t1lib around given that we have freetype. Font libraries are notoriously fragile sources of CVEs. This is a tracker for removing t1lib dependencies from as many packages as possible.
For reference, on F17: $ repoquery --qf=%{sourcerpm} --whatrequires t1lib | sort -u abiword-2.8.6-17.fc17.src.rpm dvipng-1.14-3.fc17.src.rpm evince-3.4.0-2.fc17.src.rpm grace-5.1.22-9.fc16.src.rpm gtkmathview-0.8.0-9.fc17.src.rpm perl-Imager-0.92-1.fc17.src.rpm php-5.4.5-1.fc17.src.rpm t1lib-5.1.2-9.fc17.src.rpm ttf2pt1-3.4.4-11.fc17.src.rpm xdvik-22.84.14-10.fc17.src.rpm abiword only requires it due to excessive linkage from gtkmathview's pkgconfig, the rest are quite real.
This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle. Changing version to '19'. (As we did not run this process for some time, it could affect also pre-Fedora 19 development cycle bugs. We are very sorry. It will help us with cleanup during Fedora 19 End Of Life. Thank you.) More information and reason for this action is here: https://fedoraproject.org/wiki/BugZappers/HouseKeeping/Fedora19
Adding Tracking, FutureFeature keywords to avoid rawhide rebase.
Current list of packages which are still using t1lib # dnf repoquery --qf="%{sourcerpm}" --whatrequires 'libt1.so.5()(64bit)' grace-5.1.25-9.fc27.src.rpm gtkmathview-0.8.0-19.fc23.src.rpm perl-Imager-1.006-1.fc28.src.rpm t1lib-5.1.2-21.fc27.src.rpm ttf2pt1-3.4.4-24.fc27.src.rpm
I'm not working on this and don't plan to start.