There appears to already be a branch for python-pexpect for EPEL7 but it has never been built. I've prepared a pull request to update it for Python 3.6 and remove Python 2 support: https://src.fedoraproject.org/rpms/python-pexpect/pull-request/5 If you're not willing to maintain pexpect in EPEL, I'm willing to be a co-maintainer.
Miro made me a co-maintainer, build is currently in testing.