The Python 3 subpackage python3-gearbox is missing executables available in the Python 2 subpackage.

According to the Fedora Packaging guidelines for Python [0], if a Python package that supports Python 3 installs executables into /usr/bin,  then either both Python versions of the executables should be packaged, or only the Python 3 version, depending on the functionality they provide.
(Note the "should": having Python 2-only executables is permitted, but strongly discouraged.)

Is it intentional for this particular package?

In case it is not intentional, please provide a Python 3 version of executable, or you can just switch to Python 3 if the functionality is the same regardless of the Python version. The guide for porting Python-based RPMs is available here [1] and you may refer to it for more instructions.

It's ok to do this in Rawhide only, however, it would be greatly
appreciated if you could push it to Fedora 26 as well.

If anything is unclear, or if you need any kind of assistance, you can
ask on IRC (#fedora-python on Freenode), or reply here. We'll be happy
to help investigating or fixing the issue!

[0] https://fedoraproject.org/wiki/Packaging:Python#Avoiding_collisions_between_the_python_2_and_python_3_stacks
[1] http://python-rpm-porting.readthedocs.io/