You'll have to take that up with Ubuntu.
I suspect that the issue is that Debian decided to drop support for
wxWidgets 2.8, which is required by gnuplot in order to build the wxt
terminal. IMHO that was a poor decision, and I told them so, but
obviously it's not my call.
Since Ubuntu is based on Debian, I suppose they did the same.
Based on previous back-and-forth with the Debian packagers, my understanding
is that they plan to default to the qt terminal instead of wxt.
Since the qt terminal is now better/faster/capable than either
x11 or wxt (again IMHO) that seemed an acceptable plan to me.
But if Ubuntu has dropped wxt and _not_ moved to qt to replace
it then yeah, that would be a problem.
I hope that's not the case.
Ethan