OK, Ed, I have to agree. In my current setup, I cannot display any 4 byte utf8 characters in my app that uses KMemo. However, I used to be able to display, eg, the EGYPTIAN HIEROGLYPH starting at f0 93 80 80 (in a previous install of Linux). I assume I cannot now because the font I am using does not include that range. If that is the case then your problem is not KMemo but the default font.
In other words, before you abandon KMemo (or TRichMemo) I think you need to establish that the selected font can display the range you are needing. The full 5 byte range is a very large set of characters and the vast majority of users don't want to see many more than the 3 byte ones. So, I'd expect most font designers cut some corners to save space. Perhaps ...
Davo