I was just trying to play with the systemsettings5 > display configuration > global scale parameter.
Initially, it seems to work nicely (in comparison to my current method, using font dpi modifications)
If you start konsole, you get - depending on your cursor position - single pixel black lines across the konsole window. (sometimes only line fragments and many pixels instead of a line)
My konsole config:
- black font on white background, dejaVu sans mono 9pt, smooth fonts, draw intense colors in bold
I didn't try other fonts though, but this is still very annoying for this scaling feature and does never happen by just manipulating the font dpi.
It's konsole which needs fixing, not plasmashell
(there's a bug report there, if you search konsole you should find it)
*** This bug has been marked as a duplicate of bug 373232 ***