I went back and looked at the current ARRL's band plan chart and they don't differentiate between any of the digital modes, other than to link RTTY with the digital. Only other exception is SSTV which is in the phone bands.
So, it's up to us. Looking at the ham bands charts show the dividing line between data and phone at 18.110. And of course the ARRL code practice is broadcast on 18.0975, inferring that maybe below 18.100 is for CW? Another point, from a practical POV, is that most of our rigs have a 3KHZ bandwith, and the waterfall display is dependent on the receiver's bandwidth, falling off at or near 3,000.
So, maybe, the next slot up from 18.100 is 18.103? I know that 18.097 was suggested, but that falls over the ARRL's Morse code daily broadcasts.
Another point is FT4. Has it found a home yet? There will always be 'new' modes coming at us. So what is a good strategy moving forward?
I don't know.
You guys are a whole lot smarter than me in figuring this stuff out.