wcwidth needs several enhancements:

1. interface to configure width of ambiguous chars at runtime, maybe locale dependent (see https://chromium.googlesource.com/native_client/nacl-newlib/+/master-backup/newlib/libc/string/wcwidth.c). Maybe include this into 2.
2. interface to load widths from some kind of outer source, see Emoji skin modifiers don't work #942 (comment)
   This would make it possible to overload the default width set with some custom values. Those values could be based on backend or frontend or elseone's needs.
3. Still in doubt - maybe merge wcwidth with future grapheme handling. Most of the wcwidth rules are a subset of the grapheme clustering. Once we have working grapheme handling merging them might save a lot of runtime. This is somewhat doubtful because grapheme handling might not work at an early stage with current cell based buffer model and should be added at a later stage (closer to the renderer). See also Grapheme support #1468.