Can the desktop and terminal versions of Joplin run on the same system without conflicting?
Absolutely, they store configuration in separate locations. Lot’s of people run both.
just avoid running both in same times if you use the same profile with each other
Okay. Thanks for the info!
Just to clarify, this means that if you wish to use both the desktop and terminal versions, you do need to duplicate your entire datastore... (?)
I was doing a little testing, and it sets up a non-economical pattern of disk usage:
4GB for 'joplin' (terminal application)
4GB for 'joplin-desktop'
4GB for the iCloud sync destination.
Tell that to the 64GB SSD in my Macbook Air. 
That's the deal with Apple though isn't it? You pay more for everything, what you can do is way more limited, but in exchange you get the logo of an Apple on your devices