Peppermint OS 7 was released back in June with many graphical changes. I personally did not like the font change. Before, it was better. Well, at this time I'm using Peppermint OS 7 because it's faster and it has few apps that I need. I have also tried Plasma in Peppermint OS 7 and so far it is working smooth. If you like Plasma but you're using Peppermint, then check out this article to install KDE Plasma 5 in Peppermint OS.
Peppermint OS 6 Vs. Peppermint OS 7
Peppermint OS is dedicated to provide faster computing experience. No doubt they've put their hard work to make Peppermint OS 7 even faster. I don't recommend to install KDE plasma in Peppermint if you don't want to leave lightening fast speed of Peppermint OS.
I am only doing it for fun and for my personal liking. So far after installing KDE Plasma in Peppermint OS, it is working without any problems.
KDE Plasma 5
How To Install KDE Plasma 5 In Peppermint OS
You can also install KDE Plasma in other Ubuntu based Linux distributions such as, Linux Mint 18. So just give it a try and enjoy!
$ sudo add-apt-repository ppa:kubuntu-ppa/backports
Update system -
$ sudo apt-get update && sudo apt-get dist-upgrade
Install KDE Plasma in Peppermint OS -
$ sudo apt-get install kubuntu-desktop
How To Start Peppermint OS 7 With KDE Plasma
When you boot up your system, on the login screen click the settings button from the top right and it will present you all the installed Desktop environments that you can use. As you can see in the screenshot below I have installed two more Desktop environments, MATE and KDE. Both are working great in Peppermint OS.