At this point, the only discrepancies for Fedora 25 are Gazebo 7 and OpenCV 3.1. Qt 5 versions are usually backwards compatible, so packages targeting Qt 5.3 will probably be fine forh the 5.6 or 5.7 versions in Fedora.
There’s not likely to be any package name changes between f25 and f26, so things like rosdep keys should still work normally. It would likely be safe to target f26 with the buildsystem metadata even before it’s released. Fedora 26 will officially start to “exist” at the end of February when it’s branched from rawhide - at that point, there will be f26 repositories, mock configurations, buildsystem configurations, container images, etc., making it possible to build against it in a pre-alpha state.
I will note that Fedora has a system called copr, which is similar to Ubuntu PPAs. I set up a gazebo-latest copr some time ago, to keep the latest version of Gazebo available in Fedora releases. I kind of let it slip for a while, but I am planning on building gazebo 8 in the copr for all released Fedora versions. It may be easier to point users to that repository than to package it separately.