K4YZ wrote:

The FACT is that despite similarities of various narrow band
modes, many just don't work well in close proximity to each other.
Mode specific subbands would tend to reduce those occurences of
dissimilar mode QRM.

Forgot to add:

This is not a prctical option, though. What is an "adequate"
amount of bandwidth for a mode today will, undoubtedly be way too much
or way to little tomorrow.

Skilled operators observing "Gentleman's Band Plans" remains the
prefered methodology for this.

73

Steve, K4YZ