You can run both in parallel, I wrote about it a while ago - https://f5n.org/blog/2018/i3-kde5-plasma/ https://f5n.org/blog/2018/i3-kde5-plasma/ - and actually

You can run both in parallel, I wrote about it a while ago - https://f5n.org/blog/2018/i3-kde5-plasma/ https://f5n.org/blog/2018/i3-kde5-plasma/ - and actually drafted a post about whether I'm happy with that choice (TLDR: very happy, but not sure I need KDE at all).