Emacs already has multiple "terminals" for different platforms. Qt is
really C++ oriented too, not to mention that it uses its own weird
preprocessor in addition, and Emacs is really a C app.

I agree that adding a C++ dependency is probably complicated in a project like Emacs.

It's also not truly multiplatform — a Qt app doesn't look as good as native toolkits
do on platforms other than X.

I think that is somewhat of an argument of the past. Qt styles (and ability to use css stylesheets) really allow for widgets to look just like native. See http://doc.qt.io/qt-5/stylesheet.html or http://doc.qt.io/qt-5/qstyle.html#details for screenshots examples (see QMacStyle. QWindowsStyle & friends).

Also, I'm not sure that "not looking as good as native toolkits" is really important if it simplify the implementation, but it's a big if :-)

But I disgress, as Eli said this is a pipe dream in its current form :-)

Thank you for your input.

Philippe