Installing the package on a system where "env python" resolves to python3 will this application not start because it is a python2 application. If you invoke it with python2 it will start as expected. A simple one-line patch to the ebuild will solve this problem. In python_install replace "python_doexe" with "python_doscript". Now the gentoo python magic will happen and /usr/lib64/python-exec/python2.7/pyhoca-gui will get a python2 instead of a python shebang.
Thanks for the report and patch! That is a not-so-corner case I had missed Fixed in pyhoca-gui-0.5.0.4-r1 and pyhoca-cli-0.5.0.2-r1