The `pybootchartgui` script has been removed from the app-benchmarks/bootchart2 package due to a dependency on pygtk and Python 2, from what I could understand from the Git logs.
However, most functionality is still available without pygtk by using dev-python/pycairo and Python 3. The only missing feature seems to be the interactive mode, but the only downside of it is the need of an external tool to view the generated png/pdf.
Forgive me if I'm overlooking some other reason this script was dropped that stills makes it inelegible for inclusion.
*** This bug has been marked as a duplicate of bug 808701 ***