Nope. Not happening,. GObject-Introspection doesn't work with python3 . Neither does libxml2 or libxslt, so Gtk-doc doesn't, either.
Just out of curiosity, look through Ubuntu admin scripts written in python and see if they've all been ported.
You seem to be under the impression  that most distributions are going to be able to support running Gramps4. That's absolutely not the case. As of today, only the bleeding-edge distributions like Ubuntu and Arch can run Gramps 4 without the user having to build a Gtk stack from source. It appears that Fedora 18, to be released Tuesday, will. Debian unstable (Sid), which won't be released as stable for 2 years, is still on pygobject 3.2.2. RHEL 6 doesn't even support Gtk3 at all, though that costs money and it's likely that few Gramps users will pay for it. OpenSuse is currently on 3.2.2, though they have an RPM for 3.4.2 in their repo that might make it into 12.3 in March; otherwise it has to wait for 13 in November. Aunt Martha isn't running Arch. If she isn't on M$Win, she's probably on Fedora 16 or Suse 11.