I installed the plugin in QGIS 3.4.4 on a PC (Win10) that also has QGIS 2.18.28 installed (both installed with OSGeo4W). After I installed IPython using pip install jupyter==1.0.0 qtconsole in the ...
This installs IPython as well as its dependencies. If you want to use IPython with notebooks or the Qt console, you should also install Jupyter pip install jupyter ...