Maybe some arguments of \cmidrule could be set automatically without
additional UI?
For example, if a column with a \cmidrule underneath is set to "align
center" then this should be inherited by its \cmidrule, i.e.
\cmidrule(c){...}
Also, a \cmidrule should never stretch over more than one (multi)column.
This makes possible to to have rules with small breaks in between.
See both cases here in action here:
https://tex.stackexchange.com/a/60604/36836
I know that this might not be the wanted result in all cases. But maybe
it is what is wanted in almost all cases. And once a UI gets implemented
to set these optional arguments, in the Border dialog or so, then this
could override the default as outlined above.
Daniel
