Potential issues (the results of my 5 minutes of thought)
1) Opportunity cost. Should people practice being brief, over other things (like maybe speedreading, or improving their ability to quickly read academic papers or statistics?)
1a) i.e. Academia isn't going to change, and if we want scientifically literate ideas, we will need to be better at understanding opaque, jargon-filled academic-ese, or mathy stats stuff. So maybe that's a better use of time?
1b) On the flipside, 1a is HARD to do for many people, whereas anyone can start practicing being brief without much startup costs
2) People have a limited time to write. Being brief costs time, and so does taking time to think through your ideas in more detail. (Even giving myself 5 minutes to JUST THINK feels kind of aversive to me).
Hmm. I still think brevity is a higher priority that these other things, because it will make all the other things flow faster (both for you, and for everyone around you)