The "interbreeding" definition of species you referenced is a definition applied to sexually reproducing animals.
Why do we need to define "macroevolution"? Evolution is just evolution. There's nothing really special about "macroevolution" other than the cumulative change between groups of individuals such that we would classify them as different species. For some types of life forms this separation might be more clear than for others.
Definitions aren't going to make evolution go away.
It's equivalent to a demand that one give
an "unambiguous" definition, to identify the exact
moment when day passes to night.
The blurring of lines is precisely because
of evolution. Not that a creationist would know enough
to know something so basic.
Let alone have a clue to know sonething like how
to disprove or debate evolution.
Consequentemente, there's nothing for it but to
make up something, in this case
the too clever by one half demand for the
impossible, (else ToE is defeated).
One could easily think of a lot of ways
turn that back on the perp, but such lame
rhetoric is beneath dignity.